"The administration's record on homeland security is one of insufficient funding and mismanagement," he said.

Authorities said terrorists were only days away from carrying out the plan to blow up as many as 10 airliners flying from Britain to the United States. They were about to try a test run to see whether innocent-looking explosive materials could be brought on board, U.S. officials say.

Chertoff said the code red alert for Britain-to-U.S. flights doesn't mean "that we know for a fact there are people out there who are still active."

But he added that "particularly at this stage of the arrest and the takedown, there is sufficient uncertainty about whether the British have scooped up everybody."

He called the plot "a well-advanced plan" that was in "some respects suggestive of an al-Qaida plot."

Two US government officials, speaking on condition of anonymity because the information remains secret, said British, American and Pakistani investigators are trying to determine whether a couple of the suspects attended terrorist training camps in Pakistan.

Bush and British Prime Minister Tony Blair personally followed the developing drama before it became public, with discussions in a lengthy teleconference Sunday and a phone conversation Wednesday.

Intelligence officials watched the plot unfold until they could wait no longer because of the impending test run, officials said.

A red alert for flights from Britain was the first since the color-coded warning system was developed after the Sept. 11, 2001, terror attacks. The decision to ban nearly all liquids from passenger cabins was reminiscent of the stringent rules imposed when planes were allowed back in the skies for the first time after the 2001 attacks.

All other flights to and within the United States were put under an orange, or high, alert Thursday, one step below red but up from the yellow status that had been in effect.

"No liquids or gels will be allowed in carry-on baggage," Chertoff said. "There will be exceptions for baby formula and medicines, but travelers must be prepared to present these items for inspection at the checkpoint, and that will allow us to take a look at them and make sure that they're safe to fly."

Accounts leaked by investigators described a plan on the scale of 9/11 that would use common electronic devices to detonate liquid explosives concealed in sports drink bottles.

The bombs were to be assembled on the aircraft apparently with peroxide-based solution and everyday carry-on items such as a disposable camera or a music player, two American law enforcement officials said. The officials spoke on condition of anonymity because Britain asked that no information be released.