The administration's warrantless wiretapping program looks set to be the subject of renewed and bitter wrangling between Congress and the White House when lawmakers return to Washington in September.

And this upcoming battle promises to be far more complex than a run-of-the-mill dispute over an agriculture bill, say, or tax legislation. The law in this area is unusually dense and difficult. The underlying activity is classified. One of the key administration figures dealing with the issue is Attorney General Alberto Gonzales, an official in whom many in Congress have little trust.

"Essentially, it's a difficult situation to have a rational conversation on the merits," says Benjamin Wittes, an expert on national security law at the Brookings Institution in Washington.

The expanded snooping powers of the National Security Agency (NSA) have been controversial ever since they became public in 2006. To critics, the program opens the door to the possibility of dangerous infringement on the civil liberties of US citizens. To supporters, they're a necessary tool against terrorism in an era of cellphones and Internet communications.

At issue now is the temporary update to the Foreign Intelligence Surveillance Act (FISA) passed earlier this month, just before Congress fled Capitol Hill for its summer break. This update was made necessary when the secretive judicial body that oversees the wiretapping, the Foreign Intelligence Surveillance Court, banned eavesdropping on foreigners whose communications were being routed through the United States.

The legal update, which expires in six months, allows the NSA to resume siphoning such communications. In one of its key changes, US intelligence no longer needs to know that at least one of the parties to a communication is abroad prior to eavesdropping. It needs only to "reasonably believe" that one person is off US soil.

In the weeks since this bill's passage some Democrats have begun to regret the manner in which it was approved. They feel the vote was held in haste, with summer break looming. And they've started to worry that by changing just a few words in a massive piece of law they've opened the door to practices they did not intend.

Some civil liberties experts believe that the US may now be able to gather a wide range of information from US citizens on home soil without a warrant as long as it bears upon the monitoring of a person thought to be overseas.

Nor do many lawmakers like the fact that Attorney General Alberto Gonzales is one of the key officials who will determine how the new rule is put into practice.

The bottom line: The vote will likely be revisited.

In a letter to House Judiciary Committee chairman Rep. John Conyers (D) of Michigan, House Speaker Nancy Pelosi (D) of California wrote that "Many provisions of this legislation are unacceptable, and, although the bill has a six-month sunset clause, I do not believe the American people will want to wait that long before corrective action is taken."

In addition, Sen. Patrick Leahy (D) of Vermont, chairman of the Senate Judiciary Committee, on Aug. 20 threatened to pursue contempt charges against the administration over its reluctance to produce documents outlining the eavesdropping's legal foundation.

Senator Leahy subpoenaed the NSA, the National Security Council, and the offices of the president and vice president for these papers in late June. They are necessary, he says, so that the Senate can understand better exactly what it's voting for in regard to warrantless wiretapping.

White House counsel Fred Fielding has asked for more time to respond. In an Aug. 20 letter to Leahy, however, he noted that the White House had identified a "core set" of these papers that it would likely withhold under a claim of executive privilege.

Lawyers for Vice President Dick Cheney, for instance, indicated that they had found more than 40 "Top Secret/Codeword Presidential authorizations" and memoranda dealing with the issue.

"When the Senate comes back in session, I'll bring it up before the committee," Leahy said at a press conference. "I prefer cooperation to contempt. Right now, there's no question that they are in contempt of a valid order of the Congress."

In regard to the subpoenaed documents, both sides have strong arguments for their positions, notes one legal expert.

Congress is directly legislating on the subject. In fact, eavesdropping legislation "is a critically important item on the congressional agenda," notes Carl Tobias, a law professor at the University of Richmond.

Yet courts have generally favored claims of executive privilege when they deal with issues of national security. And any move to hold the White House in contempt of Congress over the withheld documents would be slow going.

"It's hard to see that moving very far even this year," says Mr. Tobias.