He was a quiet man, diligently handing out parking tickets in Arlington after leaving a high-ranking police position for the government of South Vietnam and emigrating to America eight years ago.

But late Friday night La Van Hung, 49, walked into a Falls Church discount store, where his wife worked at a snack bar, pulled out a .38-caliber pistol and fired at least three times. Police said said yesterday that when it was all over both Hung and his 31-year-old wife were dead and a Greenbelt man she was talking to was shot in the stomach.

Police in Falls Church, a city of 7,000 that hadn't recorded a homicide since 1979, said yesterday they could offer no explanation for the shootings at the Zayre's department store on Wilson Boulevard.

Neighbors and friends were bewildered. Hung, they said, was not known to argue with his wife.

"He was a very quiet guy," said one of Hung's Arlington neighbors. "I can't believe it because that's a nice quiet man . . . ," said the man, who asked not to be named. "That is surprising, because he borrowed my car jack yesterday afternoon before 3 o'clock."

Hung, a police inspector who had studied with the FBI and at Georgetown University, once worked daily with State Department and Air Force intelligence officials before catching one of the last helicopters out of Saigon in the waning moments of the South Vietnamese government in 1975.

Like many Vietnamese immigrants, Hung with his wife and baby daughter, Thu, left Vietnam with little more than the clothes on their backs. He struggled to make ends meet in Arlington, where he first refused to go on welfare, said retired Army Col. Donn GrandPre, who was Hung's American sponsor. GrandPre, now an author who lives in Madison County, Va., had planned to mention Hung in his upcoming autobiography.

"They both worked seven days a week to become good Americans and raise their little girl, Thu . . . so she could realize the American dream," wrote GrandPre in a draft of a chapter.

"Hung was a comer," wrote GrandPre, noting that Hung took special training in the United States and the Philippines to work his way up in Saigon. "His dossier is nearly two inches thick with awards and commendations, including a special award signed by Dean Rusk, then secretary of state, for Hung's outstanding achievements in a course for police officers for many nations."

At one point after his arrival in America, Hung was so despondent over his inability to find work that he considered pawning a prize jade necklace, one of the few items he had managed to bring from Saigon, GrandPre said. But his wife, Anh Ngoc Tham, went to secretarial school and got a job as did Hung. He was hired by Arlington in 1977 as a police aide and spent most of his time writing parking tickets.

His wife later went to work at Zayre's, making money for the family's payments on the family's two-story town house in the Clarendon area, where many Vietnamese live.

Hung normally did not carry a police gun when on duty, according to friends and neighbors. Police said they didn't know where Hung obtained the pistol he took with him to the store.

When he arrived there about 10 p.m., police said, he discovered George A. Fleishell, 54, of Greenbelt talking to his wife. An argument followed, but police said they were uncertain over what. After shooting Fleishell in the stomach, Hung shot his wife in the face and then himself in the head.

Fleishell was listed in fair condition yesterday at Arlington Hospital.