Emerging from the White House where he spent the day evaluating details of an American Airlines crash in Queens, New York, President Bush sent his condolences to the families of the 255 passengers and crew.

"I too want to express my heartfelt sympathies for the citizens of New York, those on the airplane, those whose houses were damaged, those who were hurt on the ground for the recent incident that took place," Bush said, accompanied by former South African president Nelson Mandela.

Officials in Washington -- out of the office for the Veterans Day holiday -- scrambled back to their desks in search of explanations for the crash Monday morning.

Bush, in the White House at the time of the crash, cancelled his question-and-answer session with Russian and American reporters in advance of a meeting with Russian President Vladimir Putin.

Instead, he sat down with advisors to go over what little is known about the cause of the crash so far, officials said. Bush also called New York City Mayor Rudolph Giuliani and New York Gov. George Pataki to discuss recovery efforts.

"It is heartbreaking to have picked up the phone and called my friend Rudy Giuliani and Governor George Pataki and once again expressed our condolences, and at the same time, assured the people of New York our federal government will respond as quickly as possible," Bush said.

Bush was meeting with his National Security Council team about events in Afghanistan when he was handed a note at 9:25 a.m. informing him of the crash, said White House spokesman Ari Fleischer.

Fleischer said the National Transportation Safety Board was put in charge of the investigation, and the president dispatched Federal Emergency and Management Agency Director Joe Allbaugh to the crash site in Queens.

Fleischer cautioned that facts may change about what brought the plane down.

"First reports typically are the reports that change the most," he said, but added that Americans should not be afraid to fly since there is no indication that terrorism brought down the plane.

He said no cause of the crash has been ruled in or out yet, but there is no record of unusual communications between the cockpit and the tower at Kennedy airport where the flight originated.

Vice President Dick Cheney was at a secure location when the accident happened but was monitoring events, Fleischer said.  The president and vice president have been frequently separated for security reasons since the Sept. 11 attacks.

Homeland Security chief Tom Ridge, however, was in the White House at the time of the crash.  Ridge was taken to the situation room where he joined a conference call with Attorney General John Ashcroft, FBI director Robert Mueller, Transportation Secretary Norm Mineta, Allbaugh and officials from the FAA and the Pentagon.

Ridge also spoke separately with Giuliani, Fleischer said.

Federal Aviation Administration officials so far said the crash appears to be mechanical.  One official said the plane lost some radio communication, which sent fighter jets  -- already on continuous patrol in New York -- scrambling to the scene.

FBI officials at the Justice Department said they had no warnings or specific threats of an attack in New York.  The FBI backed away from earlier reports that it was investigating suggestions that the plane experienced an explosion on board, and said it was neither focusing on a bomb nor discounting that theory.

FBI officials said they were collaborating with the NTSB about the cause of the crash, but no determination had been made.

No security problems were reported this morning from Kennedy airport and the FBI has no "criminal" evidence to go on, an official said.

In Langley, Va., CIA spokesman Bill Harlow said: "All appropriate agencies are talking to each other, trying to share information" at this point.

Over at the Pentagon, officials familiar with North American Aerospace Defense Command operations said the FAA made no request to NORAD to vector additional fighter aircraft in the New York area.

Under procedures set up shortly after the Sept. 11 terror attacks, the FAA tightened communication with NORAD to report immediately any anomalies in airplane flights such as shut down transponders or off-course planes. NORAD received no such reports and keeps an Airborne Warning and Control System aerial radar plane active 24 hours a day.

Pentagon officials familiar with aviation issues said the FAA did have a loss of radio contact with the American Airlines Airbus A300, but that given the very short time the plane was in the air, that loss of contact could have been caused by the crash itself.  It will be important to exactly correlate the time of the loss of contact and the crash, officials said.

The Pentagon remains on Threat Con Charlie, a heightened state of alert that it has been on for weeks.

House Minority Leader Dick Gephardt used the accident as an opportunity to stress the need for an airport security bill that has been stuck in a House-Senate conference for nearly two weeks over the issue of federalizing baggage screeners.

"This could have been a case of a bomb in a bag that was undetected and obviously we need to have better X-ray scanners and better work on the bags that go in the top of the plane," Gephardt said.  "If we had passed the Senate bill, this bill would have been law by now and we could have started making the changes."

The Associated Press contributed to this report.