WASHINGTON - Efforts to extend the USA Patriot Act cleared a major hurdle Thursday when the White House and key senators agreed to revisions that are virtually certain to secure Senate passage and likely to win House approval, congressional leaders said.

The law - passed in the wake of the 2001 terrorist attacks, and scheduled to lapse in key areas last year - makes it easier for federal agents to secretly tap phones, obtain library and bank records, and search the homes of suspected terrorists. Several Democrats said the compromise announced Thursday lacks important civil liberties safeguards, and even the Republican negotiators said they had to yield to the administration on several points.

But with virtually all 55 GOP senators now on board, and numerous Democrats joining them, the plan appears to have enough support to overcome the Senate filibuster that has thwarted a four-year renewal of the statute for months. Senators said they believed the White House will be able to coax the Republican-controlled House to agree as well, even though House leaders have complained that senators' demands had weakened the measure.

''It was a bipartisan group of us that really believed we could do better . . . to protect civil liberties even as we gave law enforcement important tools to conduct terrorism investigations,'' Sen. John Sununu, R-N.H., told reporters. He said he and his fellow negotiators had to make more concessions to the administration than they wanted to, but that Congress will monitor the law's application over the coming years and perhaps revise it.

Sen. Richard Durbin of Illinois, one of several Democrats who agreed to back the compromise Thursday, said, ''It falls far short'' of the bill passed by the Senate last year but was rejected by the House. ''But if you measure it against the original Patriot Act . . . we've made progress'' toward ''protecting basic civil liberties at a time when we are dealing with the war on terrorism,'' Durbin said.

Senate Minority Leader Harry Reid of Nevada called the compromise ''a step in the right direction.''

The proposal would restrict federal agents' access to library records, one of the Patriot Act's most contentious provisions. A form of secret subpoena known as National Security Letters could no longer be used to obtain records from libraries that function ''in their traditional capacity, including providing basic Internet access,'' Sununu and others said in a statement. But libraries that are ''Internet service providers'' would remain subject to the letters, Durbin said.