A U.S. Capitol Police officer sobbed as she told a Prince George's County jury yesterday that the Lorton Reformatory inmate she fell in love with and married turned out to be a heavy drinker who beat her frequently. After enduring abuse and violence for several years, the officer said, she killed him with her service revolver when he threatened to attack her, because she "did not want to die."

Sharon Diane Clark, 31, testified that she was packing her clothes to move out of their Landover apartment on March 14 when her husband, Carl Henry Clark, 40, told her she was "not getting out alive." She took her revolver from her purse, she said. "He was coming after me," she said. "He had his fists bunched up . . . . He was going to kill me."

Clark spoke with difficulty between her sobs, and as she was describing how she killed her husband, she cried out loudly. Clark said she fired a single shot at her husband, and he fell to the ground.

When she touched him, she said, he was no longer breathing. He was pronounced dead four hours later, when emergency workers went to the apartment after Sharon Clark turned herself in to police.

Prosecutor Bond E. Rhue is seeking to convict the five-year police veteran of murder in the second degree--without premeditation. Defense attorney Richard Allen James argued that Clark, in fear for her life, acted in self-defense.

Clark testified that she met her husband, who was serving a seven-year sentence for armed robbery, while visiting another inmate at Lorton in June 1976.

"He was very nice," she said. "I would talk to him, and we just started out with a friendship, and one thing led to another." They were married in December 1977, while he was still in prison.

When Carl Clark was released in 1980, she said, he moved into her apartment in Landover and found a job as a social worker's assistant with the Council of Churches.

But very quickly, she said, things started to go wrong. Her husband was "nice" when he was sober, she said, but threatened and beat her when he was drunk.

"Everything I did was wrong," Sharon Clark said. "He resented the fact that I was working, making more money than he was." She said he called her names and accused her of "messing around" with other men. Soon after his release from prison, she said, he struck her for the first time.

She said she did not leave him "because I loved him . . . . I worked hard to get him out of Lorton. I wanted our marriage to work. I kept hoping and praying one day he would straighten up."

Clark told jurors she wrote several suicide notes after killing her husband. But after speaking with friends and relatives, she said she turned herself in at the nearby Seat Pleasant police station.