The trial of a U.S. Capitol Police officer charged with murdering her husband began before a Prince George's County jury yesterday, with friends of the couple testifying that they fought frequently during the five years they were married.

Sharon Diane Clark, 31, a Capitol Police officer since 1977, screamed and dropped her head on the table in front of her when her.38-caliber service revolver, with which she is accused of killing her husband, Carl Henry Clark, 40, last March 14, was introduced into evidence.

Defense attorney Richard James Allen argued that Sharon Clark acted in self-defense when she shot her husband in their Landover apartment. Defense witnesses testified that Carl Clark drank heavily and would assault his wife when he was drunk. An autopsy found that Clark, who was pronounced dead on the scene, had a blood alcohol content well above the legal level of intoxication.

Prosecutor Bond E. Rhue is seeking to convict Sharon Clark of second-degree murder -- murder without premeditation. Prosecution witnesses testified that Sharon Clark, accompanied by two friends, turned herself in at the Seat Pleasant police station four hours after the shooting and signed a four-page statement saying she shot her husband.

Sharon Clark is the third police officer to stand trial on a murder charge in Prince George's County in as many weeks. On Monday, an 11-year-vet-earn of the D.C. police force was convicted of second-degree murder for killing his brother, who was also a police officer, during an argument. Two weeks ago, another District police officer was aquitted of murdering a maintenance man who had come to his town house to change furnace filters.

Witnesses at yesterday's trial said Sharon Clark married her husband in 1977, while he was serving a sentence at the Lorton Reformatory for armed robbery. It remained unclear how the couple had met, but much testimony was introduced detailing the five stormy years of their marriage.

Calvin Day, who said he had been a friend of Carl Clark for about 10 years, said Clark "was like Dr. Jekyll and Mr. Hyde.... He was a real nice person until he got that liquor in him," and then he frequently would threaten to break his wife's neck.

At one point, Day said, Clark invited him to make love to his wife, and then report back to him. "He told me he was looking for an excuse to break her neck," Day testified.

The trial is expected to continue today, with two more defense witnesses and the defendant taking the stand.