WASHINGTON  For Representative Peter T. King, as he seizes the national spotlight this week with a hearing on the radicalization of American Muslims, it is the most awkward of résumé entries. Long before he became an outspoken voice in Congress about the threat from terrorism, he was a fervent supporter of a terrorist group, the Irish Republican Army.

“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,” Mr. King told a pro-I.R.A. rally on Long Island, where he was serving as Nassau County comptroller, in 1982. Three years later he declared, “If civilians are killed in an attack on a military installation, it is certainly regrettable, but I will not morally blame the I.R.A. for it.”

As Mr. King, a Republican, rose as a Long Island politician in the 1980s, benefiting from strong Irish-American support, the I.R.A. was carrying out a bloody campaign of bombing and sniping, targeting the British Army, Protestant paramilitaries and sometimes pubs and other civilian gathering spots. His statements, along with his close ties to key figures in the military and political wings of the I.R.A., drew the attention of British and American authorities.

A judge in Belfast threw him out of an I.R.A. murder trial, calling him an “obvious collaborator,” said Ed Moloney, an Irish journalist and author of “A Secret History of the I.R.A.” In 1984, Mr. King complained that the Secret Service had investigated him as a “security risk,” Mr. Moloney said.