HONOLULU (AP) _ Navy Lt. j.g. Richard C. Sather was buried on a grassy slope in an extinct volcano crater Friday, ending 21 years of uncertainty for the family of the American listed as missing in action in Vietnam longer than any other.

Sather, of Pomona, Calif., was shot down over North Vietnam on Aug. 5, 1964, when he was 26. He was the first American pilot to have crashed in North Vietnam.

Sather's remains were among those of seven people recently identified by the Army's Central Identification Laboratory here. The others were flown to the mainland two weeks ago for burial.

Sather's mother, Magdalena, who now lives in Hawaii, brother and two sisters looked on as Sather's remains were interred in the National Memorial Cemetery of the Pacific in extinct Puowaina Crater, better known as Punchbowl.

A ''Missing Man'' fly-over by four Navy A-4 Sky Hawk jets from the Fleet Composite Squadron One at the Barbers Point Naval Air Station broke the silence as six Navy officers carried the silver casket to the grave.

''Dick taught me that serving others is the greatest kind of freedom,'' said the Rev. Jerry Reynolds, pastor St. James' Episcopal Church in Kamuela, Hawaii, a family friend.

''Dick was humble and loving and one who cared more about others than himself,'' said Reynolds in his tribute during the 15-minute ceremony.

After a seven-member Navy squad fired a three-volley salute and a Navy buglar played taps, George Wyman, a family friend and member of the U.S. Pacific Command staff, presented the U.S. flag that draped the casket to Mrs. Sather. 

Sather's funeral came three days after a team of Americans and Vietnamese began their first joint search for the remains of U.S. servicemen in Vietnam. The team found bone fragments and what appeared to be pieces of an airplane on Tuesday in Yen Thuong, Vietnam, where villagers said a bomber crashed 13 years ago.

Mrs. Sather last saw her son when she drove him to San Diego to be shipped out on the aircraft carrier USS Constellation in May 1964. His plane was hit near Loc Chou Harbor on the second day of the United States' air raids against North Vietnam.

Mrs. Sather said she never doubted that her son died on that mission because other pilots saw his A-1 Skyraider plane crash and said it would have been impossible for him to survive.

But Mrs. Sather said she always thought his plane went down at sea and that his body would never be found.

The plane actually went down in shallow water and was recovered.

''It's kind of relief that at least you know what happened, and how, and that he was actually killed in the crash and there was no possibility of his having survived and being held captive,'' Mrs. Sather said after her son's remains were identified.

Sather grew up in Pomona. His mother moved here several years ago to be with her daughter.

Sather's remains were among those of 26 people returned by the Vietnamese in August. Nineteen of the 26 were identified in October, and the others were identified earlier this month.

There are 2,441 military and civilian personnel still listed as missing in action in Southeast Asia, of whom 1,787 are listed as missing in Vietnam. 

The United States and Vietnam were to discuss additional joint excavations, and Vietnamese officials said that country's government would help resolve the uncertainty over the fate of other missing Americans. The United States and Laos are also discussing plans for joint excavations