Donald D. Engen, 75, the director of the National Air and Space Museum who also was a decorated Navy pilot and a former chief of the Federal Aviation Administration, died yesterday in Nevada when his glider plunged to the ground from two miles up, disintegrating as it fell, authorities said.

Engen, of Alexandria, and another man were killed near Minden, just east of Lake Tahoe, about 1 p.m. Pacific time in a glider fitted with a small motor, according to the Douglas County sheriff's office. Witnesses told investigators that as the glider began spiraling down, "major portions of the wings" and other parts of the aircraft fell off, the sheriff's office said.

Engen, a former test pilot and a retired Navy admiral who served in three wars, was killed instantly, along with William S. Ivans, 89, of Incline Village, Nev., who was a holder of many glider flight records, the sheriff's office said. It was not immediately clear who was at the controls.

Engen, a World War II dive bomber pilot who sank a Japanese cruiser, held the Distinguished Service Medal and the Navy Cross, which is awarded for extraordinary heroism. He took over at Air and Space three years ago, in the wake of a controversy over display of the Enola Gay, the airplane that dropped the first atomic bomb on Japan.

Engen "labeled himself part of the fix" of the museum when he took over, "and he was," said David Umansky, a spokesman for the Smithsonian Institution, of which Air and Space -- the world's most visited museum -- is part.

Engen also was the prime mover behind plans to open an annex to Air and Space at Dulles International Airport. A target opening date in 2003 has been set for the facility, which is to provide vastly increased exhibit space for the museum's aeronautical holdings.

"He has been the guiding light behind the Dulles center," Smithsonian spokeswoman Linda St. Thomas said last night. "It was his big project."

"Don has been a wonderful director for the past three years," said Smithsonian Secretary Michael Heyman.

Calling Engen`s death a "terrible tragedy," Jane F. Garvey, administrator of the FAA, said Engen continued to offer "advice and counsel" on aviation issues and to show concern about the welfare of those who had worked for him at the agency, she said.

"People just had enormous respect for him," Garvey said.

Donald Davenport Engen, who was born in Pomona, Calif., on May 24, 1924, had flying and the Navy in his thoughts since boyhood.

When he was in the fourth grade, he told his parents that he wished to be a "naval officer and go to sea." On Dec. 7, 1941, only a few months after he entered Pasadena Junior College at 17, the Japanese attacked Pearl Harbor, and Engen got a strong push toward realizing his early ambition.

After the attack, he dropped out of college and enlisted as a seaman second class in a Navy training program, according to a memoir he published in 1997, "Wings and Warriors: My Life as a Naval Aviator."

By 1943, he was headed west across the Pacific, where he was based on the carrier USS Lexington and took part in the campaign to liberate the Philippines.

He was involved in fierce combat.

"Almost everyone experienced fear from time to time," he wrote. But, he said, "we junior pilots felt invincible, even though our loss rate seemed to indicate otherwise."

After the war, he gave civilian life a try, enrolling in the Naval Reserve and flying on weekends. That did not satisfy his passion for life in the air, and he reenlisted for active duty. Given a second chance at a Navy career, he said, "I could have walked on water."

He made a career as a test pilot, helping to develop many of the safety mechanisms that have become standard for the aviators who were to follow him.

A test he made of an ejection seat at a factory in Philadelphia left him with a compressed disc in his spine. He regarded the sacrifice as worthwhile, however, for the seat was credited with helping to save the lives of more than 6,000 pilots.

In 1950, after the outbreak of the Korean War, Engen was an officer on board the USS Valley Forge. While flying from its deck, he took part in the first aerial strike over Pyongyang, the North Korean capital.

Later, he commanded a squadron and an air wing during the Vietnam War, although he did not see action there. While serving in the Navy, he received a bachelor of science degree from George Washington University in 1968 and also attended the Naval War College.

He served as commanding officer of the USS Katmai and the USS America and of the Navy's Carrier Division 4. He was deputy commander in chief of the U.S. naval forces in Europe from 1973 to 1976 and of the U.S. Atlantic Fleet from 1976 to 1978.

He advanced through the officer ranks to vice admiral.

After retiring from the Navy in 1978, he became general manager of a division of the Piper Aircraft Corp. and in 1982 was appointed by President Ronald Reagan to the National Transportation Safety Board -- one of the agencies that is investigating his death.

Engen encountered some turbulence during his 1984-87 FAA tenure. Public attention focused on his agency in 1987, in particular, when airline passengers complained about flight delays. He warned early in the summer vacation season that delays would occur, largely because there were not enough airports to handle increased traffic.

Speaking not long after the NTSB warned that there had been "an erosion of safety" in aviation, Engen called U.S. aviation the word's safest, asserting that criticism of the system was often based on "emotion and misinformation."

In a speech at the National Press Club, the soft-spoken admiral said that the holder of his post would never lack for critics looking over his shoulder.

"There is a fine line between constructive oversight and unconstructive meddling," he said.

Engen said more airports were needed, rather than re-regulation of the airlines, as some critics had proposed.

The reasons for his resignation were not made known, but in aviation circles it was said that friction had occurred between him and then-Transportation Secretary Elizabeth Hanford Dole. The FAA is part of the Transportation Department.

Of his departure, Engen said only, "There's never a good time to leave, but the time has come."

After a long search, he was picked in June 1996 to head Air and Space. Critics had contended that the proposed Enola Gay exhibit depicted the United States as the aggressor during World War II. At the time of his appointment, one of the critics called Engen "a true aviator," and said "we are all exalted."

Engen married the former Mary Ann Baker in 1943, and they had four children.

CAPTION: Donald D. Engen was killed in a glider accident in Nevada.

CAPTION: A Douglas County, Nev., official investigates the glider crash that killed Donald D. Engen, the director of the National Air and Space Museum, and another man. The crash occurred near an airport just east of the Sierra Nevada.