WASHINGTON — The terrorist attack foiled by British authorities on Thursday was aimed at blowing up as many as 10 airplanes on trans-Atlantic flights, and plotters had hoped to stage a dry run within two days, U.S. intelligence officials said.

The actual attack would have followed within days.

One official said the suicide attackers planned to use a peroxide-based solution that could ignite when sparked by a camera flash or another electronic device.

The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, these officials said. They spoke only on condition of anonymity because of the sensitivity of the subject matter.

The details of the alleged plot surfaced as the administration posted a maximum code-red alert for passenger flights from England to the United States and banned liquids from all carry-on bags.

The security upgrade triggered long lines at airports across the country, and governors in at least two states activated National Guard troops to help provide protection.

"This was a well-advanced plan," Homeland Security Secretary Michael Chertoff told reporters as British authorities announced the arrests of 24 alleged plotters. "In some respects suggestive of an al-Qaida plot."

Los Angeles Mayor Antonio Villaraigosa said as many as 10 flights had been targeted.

Other officials said they were United, American and Continental Airlines routes from Britain to the major U.S. summer tourist destinations of New York, California and Washington, D.C. These officials declined to provide details on when the plotters intended to strike.

Virginia's deputy homeland security director, Steven Mondul, said that in a morning conference call, federal officials pointed to New York's John F. Kennedy Airport, Los Angeles International and Dulles Airport outside Washington as "major destinations for flights originating from the United Kingdom." No specific warnings were issued for these facilities, he added.

The red alert for flights from Britain was the first since the color-coded warning system was developed in the wake of the 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 afterward the Sept. 11 attacks.

"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."