Officials said the American jets scrambled routinely, as they always do when an unknown aircraft approaches U.S. territory.

Last year, the jets scrambled 104 times to intercept drug smugglers.

"Overholt had trouble getting the British jets scrambled," Hanley said.

If a dirty bomb is discovered in New York before it goes off, for example, the N.Y.P.D. Bomb Squad will most likely get to it first while federal jets are scrambling.

Others said Iraqi jets scrambled to the north to avoid combat.

Military jets scrambled to intercept a fourth plane, but it crashed in Pennsylvania before they took any action.

In a television interview, Mr. Fernandes said that Indian jets had scrambled to confront those planes but that they "ran away before our aircraft could reach them."

Why did military jets not scramble on Sept. 11?

A small private plane, its pilot apparently unconscious, raced down the East Coast on automatic controls for a thousand miles today as military jets and rescue craft scrambled in pursuit.

At 10:41, with Air Force One headed toward Jacksonville to meet jets scrambled to give the presidential jet its own air cover, Mr. Cheney was urging Mr. Bush to avoid a quick return to Washington.