If the signs of disillusionment are to be believed, an extraordinary affair in American public life may be coming to an end. Since the late 1970s, a Long Island congressman, Peter King, has been aligned with one of the most violent terrorist groups in recent European history, defying critics in his own Republican Party and elsewhere, and yet managing to prosper. Now, however, Mr. King and the Irish Republican Army appear to have come to a parting of the ways.

After years spent stoutly defending the IRA and its often bloody methods, Mr. King recently called on the group to disband and bring the seemingly endless Irish peace process to a final and successful conclusion. Frustrated with continued IRA criminality, Mr. King is now in an unaccustomed position: His stance on the IRA is tougher than that of either the British or Irish governments, although it is in lockstep with White House advisers.

The Nassau County politician, who used to travel to Belfast as often as twice a year, has not set foot in Ireland since just before the September 11, 2001, terrorist attacks. Conceding that he has "cooled on Ireland," Mr. King blames an epidemic of what he calls "knee-jerk anti-Americanism" that swept through Ireland after the invasions of Afghanistan and Iraq.

"I don't buy that it's just anti-Bush. There's a certain unpleasant trait that the Irish have, and it's begrudgery ... and resentment towards the Americans," he said in a recent interview in his Washington office.

Once a vocal and frequent House champion for the IRA's political wing, Sinn Fein, and its leader, Gerry Adams, the 60-year-old, Queens-born Mr. King has said nothing about either on the House floor in years. The politician once called the IRA "the legitimate voice of occupied Ireland," he was banned from the BBC by British censors for his pro-IRA views, and he refused to denounce the IRA when one of its mortar bombs killed nine Northern Irish police officers. But Mr. King is now one of America's most outspoken foes of terrorism.

Six weeks after September 11, 2001, he told WABC radio that the military should use tactical nuclear weapons in Afghanistan if it was believed that Islamic terrorists would deploy chemical weapons on American soil. Last year, he inflamed American Muslim groups when he said that 85% of mosques in this country have extremist leaders and that Muslims in this country were reluctant to help law enforcement.

Despite his years of support for the IRA, Mr. King has become a valued ally of the Bush administration on terrorism matters and sits on the House Committee on Homeland Security. He has won considerable praise for his role as chairman of its subcommittee on emergency preparedness - most recently for helping to steer the First Responders Bill into law. The bill aims to streamline federal grants to communities most at risk of terrorist attack.

Not so long ago, the words "Peter King" and "renegade" appeared together in many a published profile. The link resulted from the Republican's support for President Clinton before and during the impeachment crisis and his bitter spat with a former House Republican speaker, Newt Gingrich, whom Mr. King, to the delight of Democrats, once termed "political road kill."

Not anymore. These days Mr. King is a mainstream GOP loyalist, at least most of the time. He praises the current House speaker, Dennis Hastert of Illinois, and he has even made up with Mr. Bush after backing the president's opponent in the 2000 primaries, Senator McCain. When Mr. Bush visited Bob Jones University in South Carolina, an institution that is notorious in Ireland for awarding an honorary doctorate to Northern Ireland's tempestuous Protestant leader, Ian Paisley, the presidential candidate became, as Mr. King angrily put it, a tool of "anti-Catholic bigoted forces."

In recent years, Mr. King said, the GOP "made friends with me."

"Several things happened," he said. "One, Gingrich left in '98. That was a big thing for me. He really symbolized the stridency and anger in the Republican Party, while Hastert made a big difference in the Congress.

"Secondly, ever since September 11, the war against terrorism, the war against Islamic fundamentalism, has become the main issue, and I have formed a very close relationship with President Bush. I have really got to know him."

Another Republican from Nassau County, Alfonse D'Amato, the former senator, has been a friend of Mr. King's for 30 years. "He's a now-independent, respected voice in the Republican Party, someone people listen to, notwithstanding his clashes with the leadership," Mr. D'Amato said. "He's a team player - up to a point. There are some matters of principle he won't be budged on."

It was in the late 1970s that Mr. King first got involved in the Irish issue, but it struck some as an unlikely choice. His family hailed from Limerick and Galway, but apart from a great-uncle who was in the IRA in the 1920s, the Sunnyside native had no roots in revolutionary politics.

"He really didn't have a direct connection with Ireland," the longtime Nassau district attorney, Denis Dillon, said. Mr. Dillon, then a Democrat but now a Republican, was an early political ally who eventually parted company when Mr. King's advocacy of the IRA became most fervent.

In 1980, Mr. D'Amato, then the senator-elect, fulfilled a campaign pledge and went to Belfast on a fact-finding trip, taking Messrs. King and Dillon with him. It was the start of Mr. King's long entanglement with the IRA, and he took to it with the zeal of a convert.

He forged links with leaders of the IRA and Sinn Fein in Ireland, and in America he hooked up with Irish Northern Aid, known as Noraid, a New York based group that the American, British, and Irish governments often accused of funneling guns and money to the IRA. At a time when the IRA's murder of Lord Mountbatten and its fierce bombing campaign in Britain and Ireland persuaded most American politicians to shun IRA-support groups, Mr. King displayed no such inhibitions. He spoke regularly at Noraid protests and became close to the group's publicity director, the Bronx lawyer Martin Galvin, a figure reviled by the British.

Mr. King's support for the IRA was unequivocal. In 1982, for instance, he told a pro-IRA rally in Nassau County: "We must pledge ourselves to support those brave men and women who this very moment are carrying forth the struggle against British imperialism in the streets of Belfast and Derry."

By the mid-1980s, the authorities on both sides of the Atlantic were openly hostile to Mr. King. On one occasion, a judge threw him out of a Belfast courtroom during the murder trial of IRA men because, in the judge's view, "he was an obvious collaborator with the IRA." When he attended other trials, the police singled him out for thorough body searches.

During his visits to Ireland, Mr. King would often stay with well-known leaders of the IRA, and he socialized in IRA drinking haunts. At one of such clubs, the Felons, membership was limited to IRA veterans who had served time in jail. Mr. King would almost certainly have been red-flagged by British intelligence as a result, but the experience gave him plenty of material for the three novels he subsequently wrote featuring the IRA.

If Peter King helped give the IRA a respectable face in America, in Ireland and Britain the IRA's reputation as a ruthless and skilled terrorist group was solidifying. The product of street disorders in 1969 in the wake of a civil rights campaign on behalf of Northern Ireland's minority Catholic population, the IRA's violent effort to end British rule against the wishes of the majority Protestant population lasted 25 years. Despite killings by state forces and Protestant terrorist groups who favored retaining Northern Ireland's British links, the IRA emerged as the single most violent group. More than 3,600 civilians, soldiers, and policemen died in the conflict between 1969 and 1994 - the per-capita equivalent death toll in America would be nearly 700,000 - and the IRA was responsible for around half of those killings.

Ireland was no stranger to episodic political violence, but the strife in Northern Ireland was the most intense and prolonged of all. At one stage, Britain had 30,000 troops stationed there to quell the violence. Meanwhile, the IRA took its campaign to Britain - where London's financial district was twice devastated by bombs - and to mainland Europe, where British NATO bases were frequently targeted. The IRA nearly killed Prime Minister Thatcher and her cabinet with a bomb in 1984, and it assassinated prominent British politicians and members of the royal family. The IRA's primary contribution to international terrorist know-how, the car and truck bombs now commonplace in Iraq, were devised and first deployed by the IRA in Belfast in 1972. The organization also developed homemade explosives, like the fertilizer-based device that destroyed the Murrah Federal Building in Oklahoma in 1995.

Much of the conventional weaponry and a great deal of the money necessary for IRA violence came from Irish-American sympathizers. Mr. King's advocacy of the IRA's cause encouraged that flow and earned him the deep-seated hostility of the British and Irish governments. In America, official animosity was no less intense. The GOP in Nassau tried, unsuccessfully, to muzzle him, and he complained that the FBI was opening mail sent from Ireland, including letters from Sinn Fein's Gerry Adams. In 1984, the Secret Service listed him as a threat when President Reagan made a trip to Nassau County to watch a Special Olympics event.

Mr. King and the IRA made the oddest of political couples. While Mr. King was an opponent of legalized abortion, a fiscal conservative, and a prominent supporter of English First - which campaigned against federal funds for bilingual education - the IRA and Sinn Fein are close to supporting abortion rights, have campaigned to give the Irish language official parity with English, and were in a pseudo-Marxist phase when Mr. King made his alliance with them. None of that bothered the IRA's American supporters.

"People like Adams were banned from America, there was censorship in Ireland, and there was no one around who would support armed struggle," a former head of the Manhattan unit of Noraid, John McDonagh, said. "But here you had this guy whose father was an NYPD cop - a politician, a lawyer, and from Queens. We may not have liked his politics, but it was so good to have someone like that, a very credible person who spoke up for us."

As Mr. King became more outspoken in his support for the IRA he was also fashioning his political career. In 1977 he was elected to municipal office in Hempstead, and four years later he became Nassau County comptroller. His breakthrough came in 1985,and for that he could thank IRA supporters in New York.Four years before, 10 IRA prisoners had starved themselves to death on a hunger strike in protest of being denied political status by the British. Week after week during the lengthy fast, tens of thousands of Irish-Americans turned out for noisy Noraid protests - and mainstream politicians, from Mayor Koch to Senator D'Amato - lined up to speak from Noraid platforms.

In the years after the hunger strike, Noraid was a major player in New York's Irish-American politics. That was most evident in the yearly election of grand marshal of the St. Patrick's Day parade, when Noraid sympathizers were chosen each year. In 1985, the group threw its weight behind Mr. King. When he won and led the procession in top hat and tails, before an estimated 2 million spectators, the Irish government boycotted the parade. Efforts to persuade Cardinal O'Connor and the city's political establishment to follow suit failed.

"It was a battle for Irish-American hearts and minds," Mr. Galvin, the Noraid leader, said. Noraid won the battle hands down, due in no small measure to Mr. King's soaring popularity in the Irish community.

"Definitely, being grand marshal helped," Mr. King said. "It gave me an opportunity, a forum for about a month, and the fact that people in the Irish-American community now knew the name King was definitely a big plus." The proof of that came that November, when he was re-elected as Nassau comptroller against a candidate who made the contest a referendum on Mr. King's pro-IRA views. Noraid lobbied heavily for Mr. King, holding fund-raising events and publicizing his campaign in its paper, the Irish People. The following year, Mr. King signaled his wider political ambitions and ran as GOP candidate against Robert Abrams for state attorney general.

Although he lost badly, within six years Mr. King was in Congress, elected in New York's 3rd District, one of the most affluent House districts. No sooner were the votes counted than Mr. King was on a plane to Belfast, inviting Gerry Adams to his swearing-in. Mr. King arrived in Washington to a hostile reception.

"I was told before I came here that the British Embassy had been here before me, talking to Republican leaders," Mr. King said, "telling them to watch out for me."

It was the IRA that changed that. In 1994 it called a cease-fire that was the outcome of a decade of secret maneuvering by Mr. Adams, and the subsequent peace process called for substantial American government involvement. The Clinton administration realized that there were very few people in America who knew anything about Mr. Adams, and that Peter King was one of them. Suddenly Mr. King found himself in demand, invited to the White House for private chats with the president and on one occasion to a Super Bowl pizza party. As Mr. Clinton sought a foreign-policy victory in Ireland, Mr. King's lengthy flirtation with Irish terrorism was forgotten. The two men became friends and political allies. Mr. King would tell people: "Gerry Adams made me respectable."

Although the Irish peace process transformed Mr. King's image in Washington, it also tested his patience. The Good Friday Agreement was brokered in 1998 with help from the Clinton administration. It set up a power-sharing government and gave the IRA's political wing, Sinn Fein, a guaranteed seat at the cabinet table alongside Protestant politicians. Nevertheless, events moved at a glacial pace and signs persisted that the IRA might be playing a double game, agreeing to decommission its weapons but not proceeding to do so. IRA operatives were arrested in Colombia on suspicion of aiding Marxist guerrillas, angering the Bush administration; a gun-running ring was exposed in Florida, and, against Mr. King's advice, Mr. Adams traveled to Cuba to meet Fidel Castro.

Then, the events of September 11, 2001, changed everything. The attacks made it untenable for an American politician to appear to be ambiguous about political violence.

As America readjusted to a new, violent reality, peace in Ireland was dropping very slowly indeed. The Good Friday Agreement faltered into suspension, and, just after another bout of talks aimed at reviving the deal failed last December, the peace process was pitched into a deep crisis.

A bank raid in Belfast by the IRA netted $51 million, and shortly afterward IRA men stabbed a Belfast Catholic to death and then intimidated witnesses into silence - both episodes highlighting the IRA's accelerating drift into criminality. The British and Irish governments criticized Mr. Adams - Mr. Bush canceled the annual St. Patrick's Day festivities at the White House as punishment - and Mr. King called on the IRA to disband.

It is a position the congressman says he won't be budged from. "I felt strongly that since the Good Friday Agreement, the political and military should be going to the finish line, and once you reached it, the military would disband," he said. "There was no longer any rationale for the IRA."

Nor will he accept any halfway measure, such as Sinn Fein's separating from the IRA.

"I would still support Sinn Fein's right to be part of the peace process," Mr. King said, "but I would be very critical of the IRA for not disbanding. No, they have to disband. Northern Ireland is at the threshold of being a democratic society."

What will he do if, as is now speculated in Ireland, the IRA refuses to disband? "With the IRA, I will reconsider my relationship," he said. "The IRA really has to disband. Whether they do it this week or next week, they have to do it pretty soon, and if they don't, I will consider speaking out against them."

Mr. King - who lives in Seaford, Long Island, with his wife, Rosemary, and has two adult children and one grandchild - is these days more concerned about American Republicans than the Irish variety. He frets about the GOP's woeful recent electoral performances in New York. While his name is mentioned as a possible gubernatorial candidate, he says he won't run - but speculation persists that he has ambitions for a statewide post.

Saying goodbye to the IRA after the attacks of September 11, 2001, may be a necessity, but it also could be an important rite of passage in Mr. King's political journey. "I see a maturation there," said Mr. Dillon said. The Nassau D.A. was there when Mr. King began his affair with the IRA.

"He was fearless and combative," Mr. Dillon said, "and now he's familiar with the issues, he's ready to move away from former allies, and he's not afraid to do so."