The U.S. Capitol was evacuated last evening after a small plane flying at a rapid clip entered Washington's restricted airspace and prompted a scramble by federal officials to launch fighter jets and other aircraft to intercept the plane.

The urgency of the evacuation order diminished after about two minutes as the pilot of the twin-engine turboprob aircraft responded quickly to the interception and changed course, federal officials said.

Still, the intrusion -- the second in about six weeks in which a small plane violated the airspace -- disrupted a Senate vote and prompted authorities at the White House to move President Bush to a more secure location.

As a result of the recent incidents, Bush administration officials are discussing the possibility of extending the restricted airspace around Washington, said an administration official who spoke on the condition of anonymity.

"While there was no danger to potential strategic targets,'' the official said, yesterday's incident and one in May involving a plane from Pennsylvania caused concern that fighter jets might not have enough time to intercept potentially dangerous aircraft.

The Beech King Air 350, registered to Standridge Color Corp. of Social Circle, Ga., was heading southwest at 6:18 p.m. when it was intercepted by F-16 fighters that escorted it to Winchester, Va., federal authorities said.

The pilot responded "very quickly," said Mike Kucharek, spokesman for the North American Aerospace Defense Command. In that respect, yesterday's incident differed from the May 11 incident, in which the pilot of a Cessna initially failed to respond to flares launched by fighter jets or hand signals from Black Hawk helicopter crews.

Yesterday, senators were voting on a measure concerning travel to Cuba when the Capitol's alarm system of flashing white lights and whooping sirens sent them scurrying for the exits about 6:30 p.m. Lawmakers, staff members, tourists and others dashed down marble stairways and through every available exit. Outside, they followed police orders to move north, toward Union Station.

This time, however, the mood seemed more relaxed and orderly. Capitol Police officers appeared calm.

At the White House, press secretary Scott McClellan said authorities were notified about 6:30 p.m. of the airspace violation, which triggered a red alert, the highest in its security system. Bush was "relocated" to a more secure location, McClellan said without elaborating.

McClellan said the alarm was called off before a full evacuation could begin. "We started to relocate some staff," he said. "The alert level did go red, but within a matter of a couple minutes it was back down to yellow."

The pilot of the Beech King had filed a flight plan to fly from Wilmington, Del., to Defiance, Ohio, the Federal Aviation Administration said. But after takeoff at 6:06 p.m., the pilot canceled the plan and switched the plane's transponder code to indicate that he was flying under "visual flight rules," which require less interaction with air traffic control. The plane was flying about 310 mph at times, FAA officials said.

At 6:18 p.m., the plane entered the north edge of the Washington restricted airspace, a 2,000-square-mile zone that covers a large area around Baltimore-Washington International, Reagan National and Dulles International airports. It had entered the Flight Restricted Zone, a no-fly zone that encompasses a 16-mile radius around the Washington Monument, when it was intercepted by fighter jets.

The pilot's name could not be learned last night, but a Standridge Color official said the man is a pilot for the company, which makes plastics. "This was not intentional whatsoever," Hal Wells said. Wells said the pilot had dropped off employees in Delaware and was headed to Ohio to pick up other employees.

A federal official said radio communication between the pilot and authorities indicated that the pilot ended up in the restricted area while trying to avoid bad weather. The Secret Service said the pilot was released last night after questioning. An FAA spokeswoman said the matter is under investigation.

Staff writers Charles Babington, Peter Baker, Petula Dvorak and Sari Horwitz contributed to this report.

The Beech King Air 350 turboprop airplane was forced to land at Winchester Regional Airport in Virginia after straying into restricted airspace near Washington.