WASHINGTON — A near-agreement to extend the controversial USA Patriot Act was blocked Friday by an odd-bedfellows coalition of liberals and conservatives who protested that it did too little to protect Americans’ civil liberties.

The act, which gives law enforcement officials wide power to use wiretaps and to search people in the United States, was Congress’ main response to the Sept. 11, 2001, terrorist attacks.

But critics have complained that the powers it gives to police invade the privacy of citizens. Among other things, the act allows officials to examine library records and to search homes without residents knowing it.

The concerns resulted in an unusual coalition of Republicans and Democrats in the Senate and House. The lawmakers were sufficiently upset at the latest proposed revisions in the act that on Friday leaders agreed to drop immediate consideration of it, partly to avoid a threatened filibuster in the Senate over the weekend.

Congressional leaders still plan to finalize reauthorization of the Patriot Act by year’s end, but the delay was a disappointment to the White House and at least a temporary victory for civil libertarians on the right and left.

Sen. Russ Feingold (D-Wis.), one of the leaders of the movement against immediate renewal of the Patriot Act and the lone vote against the original legislation, said, “I remain committed to doing everything I can to stop any bill that does not contain adequate protections for our rights and freedoms.”

With such staunch opposition in the Senate, the bill is likely to be changed in some small way to break the logjam and beat the law’s year-end expiration date. Most likely, a change will be made to the length of time the revised law would be in effect, but it is less clear whether the measure will be modified to address other concerns.

The failure to adopt the Patriot Act conference report in the House and the Senate comes on the heels of other recent legislative disappointments for the Bush administration, such as the inability of Congress to agree this week on the annual spending bill for education, labor and health programs. And it adds to the sense that Republicans who control Congress and the White House are struggling to govern.

Lawmakers said they had raised concerns about the Patriot Act with administration officials more than a year ago, but those concerns have gone unanswered.

“I don’t think that a number of key advisers have served the president well because this is important,” said Sen. John Sununu (R-N.H.), a member of the anti-renewal coalition. “We can protect civil liberties and still fight the war on terrorism.”

The main sticking point between the House and Senate is the expiration date of the law. That is called its “sunset provision.”

Senators insisted that the law should expire in four years; the House had sought a 10-year expiration. A draft agreement put the sunset provision at seven years.

But House members and senators worried about the erosion of civil liberties insisted upon the four-year term.

“On issues as important as the civil liberties of fellow American citizens, you review it and review it on a constant basis, no matter who is in the White House or who is in the Justice Department,” said Sen. Larry Craig (R-Idaho.). “It is fundamental to the strength and the character of our country.”

Senate Judiciary Committee Chairman Arlen Specter (R-Pa.), who joined the dissenting lawmakers at a news conference, said he considered the sunset issue to be the final, most important difference between the House and Senate.

“It’s important because the sunset provision keeps the pressure on the law enforcement agencies to observe the law or else it may not be renewed,” said Specter, who had earlier threatened not to sign the final conference report if House Judiciary Committee Chairman James Sensenbrenner (R-Wis.) refused to consider the Senate’s concerns.

In addition, senators opposing many of the House provisions said there were more than enough votes to sustain a filibuster. As many as 15 Republicans and 38 Democrats were expected to oppose the conference report if it reached the floor without more concessions.

“What you see evidenced today is such a broad spectrum of political thought in Congress,” said Sen. Dick Durbin (D-Ill.), the co-author with Craig of the Senate version of the bill. “I think it should give pause to the leadership as to whether or not they should go forward with [the drafted proposals] in the Patriot Act.”

Besides concerns about the sunset deadline, many lawmakers said they were unhappy about provisions allowing law enforcement officials to search library records and business records, to search a home when its resident is not present and to issue national security letters that prevent a person from challenging an order in court that prohibits him from publicly talking about allegations against him.

Feingold said, “My concerns go way beyond the sunset. We should not allow even four more years of the violation of people’s rights with regard to their business and library records when they have done absolutely nothing wrong, without any real standard.”

A draft of the conference report, which has not been approved, would require the government to notify the target of a so-called “sneak-and-peek” search 30 days after the search, rather than within seven days, as the Senate had sought.

Some lawmakers also contended that the draft report would not provide sufficient judicial review of gag orders imposed through national security letters written by law enforcement officials.

“It requires the court to accept as conclusive the government’s assertion that a gag order should not be lifted unless the court determines the government is acting in bad faith,” three Democratic and three Republican senators wrote in a letter to the heads of the Judiciary and Intelligence Committees.

Those same six senators said the draft report would allow the government to go on fishing expeditions for sensitive personal information simply by declaring the information is relevant.

Other senators said they were extremely worried that the Patriot Act would not be renewed before the Thanksgiving recess as lawmakers rushed to leave Washington.

“We know that the Patriot Act has been largely responsible for making America safer,” said Sen. John Cornyn (R-Texas). “The Patriot Act has not eroded any of our civil liberties that we hold near and dear as Americans.”

Sensenbrenner insisted that the proposed revisions in the Patriot Act would go a long way to protect civil liberties and yet give law enforcement the authority it needs.

“This agreement also ensures our tools to fight the next Mohamed Atta intent on killing thousands of Americans are at least as tough as those to fight drug dealers and organized crime,” Sensenbrenner said, referring to one of the Sept. 11 hijackers.