The latest incidents in London have been the backdrop for passionate debate in the U.S. House of Representatives on reauthorizing key portions of the Patriot Act, a sweeping law approved by Congress after the September 2001 terrorist attacks against the United States.

For months, lawmakers from both political parties prepared for the debate on the Patriot Act, which U.S. law enforcement officials have said has been their most effective tool to prevent new terrorist attacks.

Republicans and Democrats cited Thursday's incidents in London as further proof of the terrorist threat the law was designed to confront.

"I remain confident [of] not only the resolve of the British government, led by [Prime Minister] Tony Blair, but also the resolve of the British people to stand firm against these cowards," said Republican Phil Gingrey.

"Our thoughts and prayers are with our friends in London, who, today, are coping with what seems to be a second terrorist attack in two weeks," Democrat Louise Slaughter said.

Debate on the Patriot Act highlighted significant disagreements over its provisions.

Republicans recalled that the law was approved by wide bipartisan majorities after the September 11, 2001, al-Qaida attacks, and challenged assertions by opposition Democrats that the law continues to make Americans vulnerable to violations of civil liberties.

"Not withstanding the vague and general suspicion expressed by some of its detractors, the record shows that there is no evidence whatsoever that the Patriot Act has been abused to violate American civil liberties. None whatsoever," said Congressman Jim Sensenbrenner, who chairs the House Judiciary Committee.

Democrats support giving law enforcement officials tools they need to fight terrorism, but remain unhappy with key aspects of the Patriot Act involving the power of the FBI to request and justify the need for library, bookstore and other records.

Michigan Democrat John Conyers expresses concern about the use of so-called national security letters by authorities to seize citizen's records.

"Which allows the FBI to obtain financial, telephone, internet and other records relevant to any intelligence investigation, without judicial approval," he said. "Again, this is for any intelligence investigation, which means it doesn't even have to deal with terrorism or even a crime."

Republicans, such as Michigan Congresswoman Candace Miller, say there are strong requirements for judicial review of requests, and insists terrorist threats justify the strongest of measures.

"While I care deeply about protecting the civil rights of law-abiding Americans, I do not care one iota about the civil rights of terrorists bent on destroying our way of life," said Ms. Miller.

Democrats also complain that key provisions, including two involving library, medical records, and wiretap authority, are being extended for 10 years, rather than being allowed to expire, while 14 others are being made permanent.

The question of allowing certain provisions to expire, once they are no longer needed, so-called sunset provisions, sparked a sharp exchange between two Republicans, Congressman Sensenbrenner and California Congressman Dana Rohrabacher.

"I gladly supported Patriot Act one, [but] now they have taken all but two of the sunset provisions, which would make those extraordinary new powers that we gave the government lapse once we have peace in this country," said Mr. Rohrabacher. "Any real patriot will vote against this expansion of government at the expense of the individual even when peacetime comes."

"This committee has done its job, it has done its job effectively, and it has made sure that the civil liberties of the people of this country have not been infringed upon," Congressman Sensenbrenner said.

Legislation reauthorizing the Patriot Act is also moving toward consideration in the U.S. Senate, where similar issues are being debated. President Bush has described reauthorization of the Patriot Act as vital to the war on terrorism.