The raids in Britain on Thursday followed a monthslong investigation, but U.S. intelligence officials said authorities moved quickly after learning the plotters hoped to stage a "dry run" within two days, with the actual attack expected just days after that.

The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, the officials said, speaking on condition of anonymity.

Targeted were United, American and Continental Airlines flights from Britain to major U.S. destinations, which counterterrorism officials said probably included New York, Los Angeles and Washington, D.C. Los Angeles Mayor Antonio Villaraigosa said the individuals plotted to detonate liquid explosive devices on as many as 10 aircraft.

President Bush, who has been on a working vacation on his Texas ranch near Crawford, had known about the investigation for at least several days. He received "full briefings" about the alleged plot over the weekend and had two conversations about the imminent threat with British Prime Minister Tony Blair, said White House press secretary Tony Snow.

"This nation is at war with Islamic fascists who will use any means to destroy those of us who love freedom, to hurt our nation," Bush declared.

Bush acknowledged airport restrictions would annoy travelers and urged patience.

The plane bombings could have come just ahead of the fifth anniversary of the Sept. 11 attacks carried out by al-Qaida. The terror group's leader Osama bin Laden and his No. 2, Ayman al-Zawahri, are believed hiding along the Pakistan-Afghanistan border and have repeatedly issued tapes threatening new attacks.

The close call also shifted attention once more to Britain's Islamic community just over a year after the London transit attacks. Three Britons of Pakistani descent and a Jamaican convert to Islam carried out those deadly bombings with a peroxide-based explosive that trained operatives can make using ordinary ingredients such as hair bleach.

French Interior Minister Nicholas Sarkozy said the group "appears to be of Pakistani origin," but did not give a precise source for the information. Britain's Home Office refused comment.

A British police official, speaking on condition of anonymity because of the sensitivity of the investigation, said the suspects were "homegrown," though it was not immediately clear if all were British citizens. He said authorities were working with Britain's large South Asian community.

Tariq Azim Khan, the Pakistani minister of state for information, said "these people were born and brought up in the United Kingdom. Some of them may have parents who were immigrants from Pakistan."

Raids were carried out at homes in London, the nearby town of High Wycombe and in Birmingham, in central England. Searches continued throughout the day, and police cordoned off streets in several locations. Police also combed a wooded area in High Wycombe.

Hamza Ghafoor, 20, who lives across the street from one of the homes raided in Walthamstow, northeast of London, said police circled the block in vans Wednesday and that they generally swoop into the neighborhood to question "anyone with a beard."

"Ibrahim didn't do nothing wrong," Ghafoor said, referring to a suspect. "He played football. He goes to the mosque. He's a nice guy."