Mr. Clinton was awakened at 2:35 A.M. by his chief of staff, Leon E. Panetta, who had been alerted to the 1:49 A.M. crash through a series of calls set in motion by a military aide who was sleeping in the basement of the White House residence, Lieut. Comdr. Richard Fitzpatrick. After being told of the crash, the President went back to sleep, aides said.

Mrs. Clinton returned to the family quarters this morning and watched from the Truman balcony above the diplomatic entrance as Secret Service agents, police officers and firefighters prowled the area, removing the wreckage, hosing away fuel and planting yellow flags to set off the gouge in the lawn left by the plane.

The South Lawn, where the Middle East peace pact was signed last year, was a remarkable sight today to those who had assumed that the White House had a sophisticated security system, with anti-aircraft guns and perhaps even rooftop missiles that could shield the mansion from an aerial intrusion, especially one so unsophisticated. Only 50 yards from the Oval Office, just around the corner from the Rose Garden, sat the tangle of metal, what was left of the plane's nose inches from the barred office window of the White House physician, Comdr. E. Connie Mariano, one floor below the State Dining Room. Near the Patio Furniture

The wreckage sat next to a set of white, wrought-iron patio furniture, across from the wide lawn where bleachers had been set up in anticipation of an afternoon ceremony today for the National Service plan, a ceremony that was moved. The cockpit was reminiscent of a crushed beer can, and the tail was tilted up, mostly intact. A tarpolin had been hung over the plane to conceal its identification numbers. A twisted brown aircraft seat rested in the dirt just left of the wreckage.

The scene was frightening proof of what military and security officials, planning against terrorist attacks, had long privately believed: that the White House is more vulnerable than anyone admits.

Judging from what happened today, either someone made a terrible security mistake or the integrity of the "secure" air space around downtown Washington -- one nautical mile on either side of the White House, extending up to 18,000 feet, and broadening to envelope the Mall, the Capitol and most of the area's well-known monuments and museums -- depends on intruders playing by the rules.

Passers-by can often see Secret Service agents walking on the White House roof or on duty in an observation post there. But experts said it would be dangerous to fire missiles in downtown Washington. A hit might send an aircraft crashing into a nearby landmark, like the Hay Adams Hotel or the Treasury Department. And, as a senior White House official noted today, "If you missed, E Street becomes pretty ugly, pal."