Efforts to extend a modified version of the USA Patriot Act reached an impasse yesterday when House and Senate negotiators could not agree on whether to renew its key provisions for four years or for seven. Some lawmakers predicted the differences will be resolved next month, before the act expires Dec. 31, but others raised concerns about the delay.

The measure, enacted after the Sept. 11, 2001, terrorist attacks, expands law enforcement agencies' ability to secretly gather information on suspects through wiretaps, subpoenas and other means. Some House and Senate members said they fear that the delay will give the bill's critics -- most notably civil liberties groups -- time to mount opposition during the two-week congressional recess that starts Monday.

The Bush administration has tried to bring the two chambers together, with White House Chief of Staff Andrew H. Card Jr. traveling to the Capitol on Thursday to huddle with top negotiators. But more than a dozen senators and House members from both parties announced yesterday that they will oppose the version offered by a House-Senate conference committee, employing a Senate filibuster if necessary.

They received a major boost when they were joined by Sen. Arlen Specter (R-Pa.), chairman of the Senate Judiciary Committee, which has jurisdiction over the bill. "The key sticking point, as I see it, is the sunset provision," Specter said. "The House wanted 10 years; the Senate bill provided for four." A seven-year extension would split the difference, he said, but "there ought to be a four-year sunset so we can review it again in a reasonably timely fashion."

House Judiciary Committee Chairman F. James Sensenbrenner Jr. (R-Wis.) expressed disappointment in the impasse. "This agreement permanently tears down 'the wall' that prior to 9-11 prohibited the sharing of information between the law enforcement and intelligence communities and hindered their ability to 'connect the dots,' " he said in a statement. "I am concerned the recent snag . . . gets us a little closer to rebuilding 'the wall.' "

Some conservative Republicans on Specter's committee also bemoaned the delay. "This is a very risky thing," Sen. Jeff Sessions (R-Ala.) said in a floor speech. "We should complete this work today."

Sen. Jon Kyl (R-Ariz.) said of those holding up a resolution of the House and Senate versions, "They're about to the let the Patriot Act expire because they have some view that every little thing that they want has not gotten accomplished."

The proposed renewal of the act modifies some of the provisions that civil libertarians, on the political left and right, have criticized most sharply. Government agencies could continue to subpoena library and business records of suspects without their knowledge. But the revised version would require the agencies to specify how the request is connected to an investigation, and the library or business in question could seek a judicial review.

No longer can "a law enforcement officer unilaterally go and get their records," Specter said.

The revised bill also would make changes to national security letters, which investigators have used to demand records from suspects while ordering them to notify no one. The new measure would allow the recipient to contact a lawyer and seek a judicial review. Specter called it "an enormous improvement on the national security letters."

But some civil liberties groups, including one headed by former representative Bob Barr, a conservative from Georgia, disagreed. The new version "gives the appearance of compromise without actually doing anything meaningful to safeguard ordinary Americans' Fourth Amendment right to privacy," Barr said. "Some of these cosmetic changes simply make explicit what the law already requires and other changes in fact represent a setback for civil liberties."

Most troubling, Barr said, "the government would still not be required to provide any evidence connecting an individual to a suspected foreign terrorist before going on a fishing expedition through that individual's sensitive personal records."

Sen. Arlen Specter (R-Pa.), left, chairman of the Senate Judiciary Committee, joined lawmakers threatening to filibuster the House-Senate conference committee's proposal for an extension of the USA Patriot Act. He said the sunset provision was the main contention.