'This terrorist surveillance programme has helped prevent terrorist attacks,' Bush said in his State of the Union speech. 'It remains essential to the security of America.'
'If there are people inside our country who are talking with al- Qaeda, we want to know about it because we will not sit back and wait to be hit again,' Bush said, drawing cheers and applause from both houses of Congress gathered in Washington for his policy speech.
The monitoring programme run by the super-secretive National Security Agency (NSA) has come under heavy criticism since its existence was revealed by The New York Times in December.
Congress has vowed to investigate the programme to ensure it does not violate US privacy laws. Bush insisted Tuesday that previous presidents have taken similar steps to protect US citizens and that those efforts were upheld in court.
Bush's authorization allows the NSA to listen in on conversations involving suspected terrorists - even if one of the parties is located in the United States.
Many opposition Democrats and some members of Bush's Republican Party have questioned the programme's legality. The Senate Judiciary Committee has already announced that it will hold a hearing.
Senator John Rockefeller, the ranking Democrat on the Intelligence Committee, told Deutsche Presse-Agentur dpa Tuesday that he has been discussing an additional investigation the panel's chairman, Republican Senator Pat Roberts.
Bush also called on Congress to renew the controversial Patriot Act, which was enacted following the September 11, 2001 terrorist attacks and gives the federal government broader powers to carry out investigations.
'I ask you to reauthorize the Patriot Act,' Bush told the joint session of Congress.
Sixteen provisions of the Patriot Act were set to expire at the end of 2005. Bush wants a permanent extension of these provisions, but the Senate only agreed to a temporary extension last month because of concerns that the law infringes on civil liberties. The extension expires Friday.
The Patriot Act passed with only one dissenting voice in the Senate in 2001, but since then strong opposition to some provisions of the law has arisen.
