A corporate helicopter, climbing after taking off from National Airport for a flight to New Jersey, crashed yesterday near the intersection of the field's two main runways, apparently because its engine failed.

The helicopter's occupants, two pilots and two executives of the New York-based Pfizer pharmaceutical company, walked away from the wreck.

The airport was closed for about 20 minutes and flight delays of several minutes occasioned by the closing continued for several hours, an airport spokesman said.

The helicopter "went about 70 feet in the air, with a trail of white smoke coming out of the engine," said Steven A. Warren, a Michigan transportation expert who saw the crash while waiting in the Piedmont Airlines terminal for a trip back to Grand Rapids. "It started tilting back and forth and losing altitude fast. Then it just plopped on its belly.

"Everybody just gasped and started praying there would be no fire," he said, adding that the group joined in counting aloud as they watched figures emerge from the wreckage.

The French-manufactured Aerospatiale Dauphine helicopter appeared to be damaged on one side, with its rotor blades snapped and askew.

"Apparently the engine quit on takeoff and they had a rather abrupt landing," said Tony Biesada, a Pfizer spokesman. "No one was hurt and none went to the hospital, but the pilots were shaken up."

The only slight injury was to Bob Behnke, one of the pilots, who had a cut on his nose, said David Hess, a spokesman for the airport.

The helicopter was bound for Mercer County Airport outside Trenton, N.J., after picking up Donald C. Lum and Ed Bessey, two Pfizer executives who had had meetings in Washington, Biesada said.

When the aircraft took off from a helicopter pad near the Butler Aviation hangar at 2:18 p.m. and headed to the northeast, it was not snowing and the wind was not blowing hard, witnesses said.

Brad Dunbar, a spokesman for the National Transportation Safety Board, said that an investigator from the board is looking into the accident, a routine move in such a mishap.

He said that the cause of the crash is not yet known, but that officials of the safety board have their suspicions.

"When a guy has to abort a takeoff and there's no weather condition involved, obviously the prime suspect area is the helicopter's power," Dunbar said. "That doesn't take an expert."