With Congress at an impasse over the government's spy powers and intelligence, congressional officials are bracing for the possibility that the government may have to revert to old rules for terrorist surveillance, which some officials predict could leave worrisome gaps in intelligence.
That prospect seemed almost inconceivable just a few months ago, when congressional negotiators and the White House promised a quick resolution to a bruising debate over the government's surveillance powers. But the dispute has dragged on. Though both sides say they hope to reach a deal, officials have been preparing classified briefings for Congress on the intelligence ''degradation'' that they say could occur if no deal is reached by the summer.
The deadline is considered critical because of a series of secret one-year wiretapping orders approved last August under a temporary wiretapping law. The law allowed the National Security Agency to use broad blanket court orders against groups of suspected Qaeda terrorists based overseas. But those orders are growing staler by the day, officials said, and will begin to expire this August if nothing is done.
''We'll start losing intelligence capabilities,'' Senator Kit Bond of Missouri, the ranking Republican on the Intelligence Committee, said in an interview.
Civil libertarians who oppose the government's broadened new surveillance authority said a return to the more restrictive rules might be just what was needed to restore necessary checks on the government's powers.
But government and congressional officials said in interviews that they saw that possibility as a dangerous step backward. A return to the old rules, they said, would mean that numerous government lawyers, analysts, and linguists would once again have to prepare individual warrants, potentially thousands of them, for surveillance of terrorist targets overseas.
Telecommunications companies would also have to spend considerable time shutting down existing wiretaps and then to start them up again if ordered under new warrants, officials said. In some instances, the broad orders given to the companies starting last August cover tens of thousands of overseas phone numbers and e-mail addresses at one time, people with knowledge of the orders said.
A senior intelligence official, speaking on condition of anonymity, said the administration was concerned that reverting to the older standards and requiring individual warrants for each wiretap would create a severe gap in overseas intelligence by raising the bar for foreign surveillance collection.
In some cases, the government might simply be unable to establish in court why it suspected that a foreign target was connected to terrorism. Part of the problem, officials said, is that communications from one foreign country to another sometimes travel through a telephone switch on American soil and, under some interpretations of the older rules, could not be tapped without an individual warrant.
Wiretaps aimed at Americans already require individual warrants issued by a secret court, known as the Foreign Intelligence Surveillance Act, or FISA, court.
Attorney General Michael Mukasey has called reversion to the older standards of foreign surveillance ''unthinkable,'' adding, ''I still hope and actually think that it won't happen.'' Even some Democrats, at odds with the White House for months over the surveillance issue, said they were worried about the outcome. ''Until August, we're O.K.,'' said a senior Democratic congressional aide involved in the negotiations. ''After August, we're not O.K.''
A second Democratic congressional official, who also spoke on condition of anonymity, said: ''We don't even want to get close to the expiration, because it will force the intelligence community to make preparations and transition back to the old system. Having to go back to the old way of doing things is problematic.''
Congress began debating the agency's spy powers in December 2005, after it was disclosed that President George W. Bush had authorized the agency to conduct wiretaps without court warrants on the international communications of Americans suspected of terrorist ties.
The current stalemate on the issue reflects deep divisions in Congress over how to suture the wounds created by the wiretapping program. Few people in Washington thought the debate would drag on this long, through dire warnings from the White House about potential harm to national security, through retreats and push-backs by the Democrats and now through a game of chicken over how to resolve the impasse.
''I was hoping we'd made progress,'' said Bond, who has been the White House's point man in the negotiations. ''But the longer this drags on - I'm not so sure.''
Democrats and Republicans have been negotiating behind closed doors for months, with occasional appearances by senior administration officials. The main stumbling block has been whether or how to give the phone companies immunity from lawsuits over their role in helping Bush's warrantless wiretapping program; dozens of such suits are pending. Both sides have given some ground in the talks.
The Republicans have yielded somewhat on immunity for the companies: The current proposal from Bond would allow the FISA court to review the administration's requests to them and determine by a ''preponderance of the evidence'' whether the companies had acted properly in response.
Bond's proposal would also re-establish that the act is the ''exclusive'' means for authorizing intelligence wiretaps, even in the face of Bush's claims of constitutional authority to order surveillance on terror suspects outside the courts. And it would allow for a congressional review of the wiretapping program, something Republicans had tried to avoid.
House Democrats, meanwhile, appear willing to settle for the FISA court's having a smaller oversight role in approving the National Security Agency's surveillance procedures in advance. They offered a counterproposal to Republicans late last week that left both sides optimistic.
In fact, though, every week over the past four months has brought talk of a pending deal on Capitol Hill that soon collapsed again. Mukasey said that Justice Department negotiators ''come in and talk to me and are sort of more optimistic and less optimistic from minute to minute, and I try to not have my mood go up and down.''
As hard as the White House has pushed on the issue, Democrats may have even more at stake. They acknowledge not wanting to risk reaching their national convention in Denver in August without a deal, lest that create an opening for the Republicans and Senator John McCain, the Republicans' presumptive presidential nominee, to portray themselves as tougher on national security - a tried-and-true attack method in the past - just as the Democrats are nominating Senator Barack Obama.
Bush used that line of attack repeatedly in January and February, imploring Congress to renew the broadened spy powers it had granted the agency last August. The surveillance plan was essential, Bush said at the time, because terrorists were planning attacks on American soil ''that will make Sept. 11 pale in comparison.''
Despite the president's pleas, House Democrats refused to buckle, a rare instance in which they stood their ground against Bush on a matter of national security. They allowed the August law to expire in February.
Caroline Fredrickson, who leads the American Civil Liberties Union's Washington office, said Democrats should continue to resist the White House's pleas for broadened spy power, even in the face of political pressure.
A return to the older surveillance rules, requiring individualized warrants for all wiretaps, would be a positive step, she said. The last thing Congress should do, she added, is enact a major overhaul of the nation's spy powers just before Bush leaves office.
''Why not just kick it down the road'' through a short-term extension, she asked. ''If there's a need to do something, they should do the least harm possible.''
''We don't think this Congress should give President Bush the gold watch he's looking for in authorizing his warrantless wiretapping program,'' Fredrickson said.