Democrats in the US Senate, along with several rebel Republicans, blocked passage of a new Patriot Act to combat terrorism on Friday, by 52 votes to 47.
The vote fell eight shy of the 60 needed to end the debate. The current act expires on 31 December and Republicans have rejected a call for a short-term measure to prevent the expiration.
President Bush said in his weekly radio address from the White House: "In the war on terror, we cannot afford to be without this law for a single moment. That decision is irresponsible and it endangers the lives of our citizens. The senators who are filibustering must stop their delaying tactics and the Senate must reauthorise the Patriot Act."
Threat to liberties
The Patriot Act was introduced in the days after the 9/11 attacks in New York in 2001. Critics of the act, many of them Democrats, claim it is a threat to the constitutional liberties of innocent Americans.
Much of the controversy over the new proposals involves powers that would allow law enforcement agencies to gain access, in secret, to a wealth of personal data, including library and medical records.
The bill gives the authorities
in the US extended powers
The bill includes a four-year extension of the government's ability to conduct roving wiretaps and the authority to wiretap "lone wolf" terrorists who may operate on their own, without control from a foreign agent or power.
Another provision, which applies to all criminal cases, gives the government 30 days to provide notice that it has carried out a search warrant. Current law requires the government to disclose search warrants in a reasonable period of time.
The debate has been intensified by a New York Times report that Bush had secretly authorised eavesdropping on individuals in the United States without first gaining permission from the courts.
Most Republicans and the act's other supporters say the law is essential for protecting the country against terrorists.
Of the 55 Republicans in the Senate, four helped to block its passage while two of the 45 Democrats pushed to pass it.
If the law is not renewed, its powers will expire on 31 December for new investigations of people whose criminal activity began after 31 December and who were not associated with anyone who was under investigation before 31 December.