WASHINGTON -- A bipartisan group of senators blocked a final vote on changes to the USA Patriot Act yesterday, arguing that the legislation did not go far enough in protecting civil liberties.

The failure of Republican leaders to secure enough votes to defeat a filibuster was a sign of growing concern in some parts of the country that the government went too far in empowering law enforcement after the Sept. 11, 2001, domestic terror attacks. It was a dramatic shift from the initial vote on the Patriot Act that year, when only one senator voted against the legislation.

The refusal by 46 senators to end debate on the act's renewal led to a standoff yesterday between Republican leaders allied with the White House and senators of both parties who want more time to make changes to the House-Senate compromise. Supporters needed 60 votes to end debate and proceed to a vote on the reauthorization.

Republican Sens. Arlen Specter and Rick Santorum of Pennsylvania and Mike DeWine and George Voinovich of Ohio were among those who voted to end debate, while Democratic Sens. Robert Byrd and Jay Rockefeller of West Virginia opposed the cutoff.

Senate Majority Leader Bill Frist, R-Tenn., yesterday refused two attempts by Democratic senators to approve a three-month extension of the current Patriot Act that would have given the House-Senate panel more time to negotiate improvements to the compromise.

In his refusal, Mr. Frist was backing the Bush administration. White House spokesman Scott McClellan said President Bush "made it very clear that he was not interested in signing any short-term renewal" and would let the Patriot Act expire Dec. 31 -- a tactic intended to force senators to change their vote in the next 24 to 72 hours.

Mr. Bush said in a statement that "the Congress has a responsibility not to take away this vital tool that law enforcement and intelligence officials have used to protect the American people" and urged senators to give up their delaying tactics so Americans are "not without this critical law for even a single moment."

Though four Republican senators -- Larry Craig of Idaho, Chuck Hagel of Nebraska, Lisa Murkowski of Alaska and John Sununu of New Hampshire -- joined Democrats in refusing to halt debate, GOP leaders criticized the vote as partisan. Some said the legislation's foes were jeopardizing national security.

"God help us if there is some kind of terrorist attack when we are not protected by the Patriot Act," said Sen. Jon Kyl, R-Ariz.. "For our colleagues to allow [the Patriot Act] to expire is to play with fire. It is to take the chance that terrorists will not act in that interim, in that period where the act falls and we're relegated to using the authorities that we had before September 11th."

But those who supported the filibuster said that if the act expires, responsibility will fall squarely on the shoulders of Republican leaders who have blocked extension of current law.

"I hope that everyone who says the Patriot Act is an important piece of legislation is willing to extend the existing provisions while we work out these differences," Mr. Sununu said. "Anyone that would be opposed to that obviously doesn't quite think it's that important."

Coloring yesterday's debate was the revelation in The New York Times that President Bush had signed a secret order in 2002 permitting the National Security Agency, or NSA, to monitor international phone calls and e-mails of hundreds of people within the United States without getting court approval.

The president's order was not linked to the Patriot Act, but Democratic senators raised the issue repeatedly during the debate as an example of unchecked executive branch power. Sen. Charles E. Schumer, D-N.Y., said he had considered voting for the House-Senate Patriot Act proposal until he saw The New York Times story yesterday.

"If this government will discard a law that has worked well for over 30 years without a wit of discussion or notice, then for sure we better be certain that we have safeguards on that government," Mr. Schumer said. "Today's revelation makes it crystal clear that we have to be very, very careful."

Mr. Specter, who negotiated for the Senate in House-Senate deliberations regarding the Patriot Act, said The New York Times story was "very, very problemsome, if not devastating" to his efforts to gain passage of the reauthorization.

Objections to the House-Senate compromise that Mr. Specter helped to negotiate centered on two provisions.

One section lets the FBI get court orders to obtain business records such as phone logs. The renewal proposal creates new requirements for the FBI to show that the records "are relevant to an authorized investigation" related to international terrorism or spying. There is no such language in the existing Patriot Act, but lawmakers citing civil liberties concerns said the law should be more explicit so that recipients of FBI requests for business records can challenge the gag order that bars discussing the request.

The other controversial section is new wording regarding so-called "national security letters" that the FBI can send to businesses without a court order, demanding that they hand over communications or financial records of customers without the customers' knowledge.

The compromise would add a new provision making clear that people receiving these letters can consult a lawyer and ask the court to quash the FBI request if a judge decides it is "unreasonable, oppressive or otherwise unlawful." But those supporting the filibuster objected that such a standard was too high for a typical business or citizen to prove.

When the Patriot Act renewal passed the House, 251-174, earlier this week, 44 Democrats supported the compromise. Among Western Pennsylvania lawmakers, Republican Reps. Phil English of Erie, Melissa Hart of Bradford Woods, Tim Murphy of Upper St. Clair and Bill Shuster of Blair supported passage. Democratic Reps. Mike Doyle of Swissvale and John Murtha of Johnstown opposed it. Rep. John Peterson, R-Venango, was listed as not voting.