The body of John C. Bennett, 56, a White House aide who was official custodian of the Nixon tapes during the final year of the Watergate scandal, was found Monday in the wreckage of the private plane he had been piloting near Anchorage, Alaska.

Officials said Mr. Bennett, a retired Army major general, disappeared on a flight Sunday night. The wreckage of his burned plane was found 1,500 feet up Mount Susitna about 30 miles northwest of Anchorage.

Mr. Bennett retired from the Army after 27 years of service in 1972. In June, 1973, a year after the break-in at the Democratic National Committee headquarters at the Watergate office building that started the Watergate scandal, he joined the White House staff as an assistant to Gen. Alexander Haig, the president's chief of staff.

The existence of the secret tapes that President Nixon made of his White House conversations became known on July 16, 1973. On July 18, 1973, the tapes were entrusted to Mr. Bennett.

Late in 1973, he testified before U.S. District Judge John J. Sirica that Rose Mary Woods, Nixon's personal secretry, had told him that an 18 1/2 -minute gap existed in one tape of White House conversations a few days after the Watergate break-in.

Under querstioning by Sirica, Mr. Bennett said he could not vouch for the security of the tapes, or who had access to them, before they were placed in his care. He said he had signed them out to Woods and others on orders from Nixon. He said his own system for keeping them involved putting them in envelopes that he marked in a secret way so that not even his secretary could get at them without his being aware of it. He said the envelopes were kept in his office safe. The tapes eventually played a key role in forcing Nixon to resign.

Mr. Bennett returned to Alaska after his White House service and was executive director of Alaska in 1934, a proposed trade exposition, at the time of his death. He had served in Alaska during his Army career and had been in business there before working at the White House.

Mr. Bennett was born in Washington. He attended Emory University in Atlanta, and graduated from the U.S. Military Academy at West Point in 1945. He also held master's degrees from George Washington and Columbia universities. His last assignment in the Army was as commanding general of the 4th Infantry Division and commanding general of Fort Carson, Colo. He then moved to Anchorage to begin his business career.

Survivors include his wife, the former Jean MacKenzie of Anchorage, and two sons and two daughters.