The House is set to vote today on extending the law until March 10 rather than let it expire Friday. The Senate was expected to follow before the deadline.
It would be the second time Congress has extended the law. Originally passed five weeks after the Sept. 11, 2001, terrorist attacks, the Patriot Act was due to expire Dec. 31.
Just before leaving for Christmas, Congress extended the law until Feb. 3 because Senate Democrats and four libertarian-leaning Republicans blocked a final vote on a measure negotiated by the White House that would have made most expiring provisions permanent. The Republicans were concerned about excessive police powers.
The 2001 law makes it easier for federal agents to gather and share information in terrorism investigations, install wiretaps and conduct secret searches of households and businesses.
Objections to the compromise last fall centered on the degree to which people and institutions that receive National Security Letters - secret requests for phone, business and Internet records - can appeal them in court.
Sens. Larry Craig, R-Idaho, and John Sununu, R-N.H., say the law makes it nearly impossible to challenge NSLs and their secretive demands for information.