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.''