WASHINGTON – The Senate passed a six-month extension of the USA Patriot Act late yesterday night, hoping to avoid the expiration of law enforcement powers deemed vital in the war on terror.

Approval came on a voice vote, and cleared the way for a final vote in the House.

Several provisions in the current law expire December 31, and President Bush has called repeatedly for new legislation.

The House was scheduled to reconvene today, but senior Republicans there have opposed any temporary extension of the current law, insisting that most of the expiring provisions should be renewed permanently.

The Senate vote yesterday night capped several days of backroom negotiation conducted against the backdrop of presidential attacks on critics of the legislation.

The extension gives critics – who successfully filibustered a House-Senate compromise that would have made most of the law permanent – more time to seek civil liberty safeguards in the law. Democrats and their allies had originally asked for a three-month extension, and the Senate’s Republican majority had offered a one-year extension. The final deal split the difference.

“For a lot of reasons, it made the most sense, given that there are significant differences that remain,” said GOP Senator Sununu of New Hampshire, one of a small group of Republicans who joined with Senate Democrats to filibuster a House-Senate compromise.

“I think this is a reasonable conclusion,” said Senator Leahy of Vermont, the ranking Democrat on the Senate Judiciary Committee.

Republicans who had pushed for legislation that would make most of the expiring provisions permanent said the agreement only postpones the ongoing arguments over the Patriot Act for six months. “We’ll be right back where we are right now,” said a clearly frustrated Senator Hatch, a Republican of Utah.

Senator Cornyn, a Republican of Texas, added, “Our intelligence and law enforcement officials should not be left wondering, yet again, whether the Congress will manage to agree to reauthorize the tools that protect our nation.”

The bill’s critics gained momentum Wednesday when they released a letter crafted by Mr. Sununu and Senator Schumer, showing they had 52 senators agreeing to support a three-month extension.

“This is the right thing to do for the country,” Mr. Schumer said after the deal had been announced. “To let the Patriot Act lapse would have been a dereliction of duty.”

President Bush, Attorney General Gonzales, and Republican congressional leaders have lobbied fiercely to get the House-Senate compromise passed, and issued dire warnings of what would happen if the Patriot Act expires.

Most of the Patriot Act – which expanded the government’s surveillance and prosecutorial powers against suspected terrorists, their associates and financiers – was made permanent when Congress overwhelmingly passed it after the September 11 terrorist attacks on New York City and Washington.

Making permanent the rest of the Patriot Act powers, like the roving wiretaps which allow investigators to listen in on any telephone and tap any computer they think a target might use, has been a priority of the Bush administration and Republican lawmakers.