WASHINGTON — Congress slowed the renewal of a central part of the administration’s war on terror late last week amid a standoff over how long to extend the USA Patriot Act and a filibuster threat by senators who want to curb powers the law would grant the FBI.

“I believe that more time is necessary,” said Senate Judiciary Committee Chairman Arlen Specter, R-Pa., “The bill is not now generally understood because of its volume and because of not enough time to really digest the changes.”

Specter said a compromise is reachable when Congress returns in December from a two-week Thanksgiving vacation.

A bipartisan group of lawmakers declared victory, saying they had gathered enough votes to block GOP leaders from forcing a vote on a proposal put forth by negotiators trying to merge House and Senate versions of the bill. The Patriot Act provisions expire Dec. 31 if not renewed by Congress.

“This is an issue that we need to see the fine print on,” said Sen. Larry Craig, R-Idaho. “I think there is ample time.”

Most differences between the House and Senate versions of the bill had been bridged when lawmakers supervising the effort to merge them met last week. But differences emerged on whether provisions governing wiretapping and other FBI information-gathering should be extended for another seven years or just four years.

Specter said on Nov. 18 that bridging that gap had proved the stickiest point. He said House Judiciary Committee Chairman James Sensenbrenner, R-Wis., didn’t want the provisions to “sunset” until 2012, a presidential election year.

Sensenbrenner said seven years simply splits the difference between 10 years in the bill the House passed and four years in the Senate version.

Beyond the sunset issue, some senators griped that the compromise draft removed a Senate proposal that would mandate judicial reviews when authorities used the law to search financial, medical, library, school and other records.