U.S. Responded to Plot With Speed, Secrecy

"As things headed south," one official said, Chertoff "flipped the switch" to gain approval for raising the threat level. Late Wednesday and into Thursday, DHS leaders held a series of conference calls with governors' offices, airlines, airline security specialists, labor unions, and airport security directors across the country to share information and plans.

Chertoff joined the 8 p.m. call with the security directors, saying this moment was the reason they did their jobs. Shortly afterward, TSA issued its official "security directive" banning all liquids and gels from carry-on luggage, giving airports and airlines about four hours on the East Coast to prepare more trash bins, print fliers and call in reinforcements.

Consultations with key members of Congress were held that night, bulletins were sent to law enforcement officials, and state and local homeland security officials were briefed at about 1 a.m. At 2:38 a.m., the department released a statement by Chertoff announcing a change to the threat level for the aviation sector, taking effect at airports at 4 a.m.

Knowledge of the British probe varied among local and state governments. D.C. Mayor Anthony A. Williams (D) did not know about the investigation until he was notified of the arrests. Baltimore Mayor Martin O'Malley (D) got the telephone call at 3 a.m. from the Baltimore Police Department's intelligence division.

Senior officials at the Virginia State Police already knew about the British investigation, according to police spokeswoman Corinne Geller, though she declined to elaborate. Robert P. Crouch, Virginia's top homeland security adviser, was roused by cellphone at 12:30 a.m., alerting him to a 1 a.m. conference call about the arrests with senior DHS officials and his state security counterparts.

In New York, officials said they learned about the British probe several weeks ago and were told early last week -- by British contacts -- that arrests were imminent. The city police department has an extensive intelligence operation, including officers assigned to Scotland Yard and other locations overseas.

The arrests were carried out as Bush was taking a working vacation at his ranch in Texas. Aides said he and Vice President Cheney had been kept closely informed of developments starting Aug. 4, and were regularly briefed in the days leading to the arrests.

Bush spoke with British Prime Minister Tony Blair in a 47-minute videoconference last Sunday, a conversation that the White House at the time described as being about the Middle East. The two leaders spoke again by telephone on Wednesday.

Officials said Bush's homeland security adviser, Frances Fragos Townsend, called the president late Wednesday afternoon to tell him that British authorities were poised to begin making arrests. The two stayed in touch through several phone conversations for the rest of the day, as suspects were being rounded up.

Later that evening, Bush approved the plan to elevate the nation's threat level. He retired for the night as the arrests were continuing, officials said.

Staff writers Sara Kehaulani Goo and Del Quentin Wilber in Washington, Michael A. Fletcher in Crawford, Tex., Michael Powell in New York, Michael D. Shear in Richmond and researcher Julie Tate contributed to this report.