There was standing room only on Metro's A-2 yesterday morning as the bus stopped at 9th and Bellevue streets SE to pick up a few sleepy-eyed passengers.

Among those boarding were Barbara Williams, a 23-year-old guidance aide at Hart Junior High School, and a man. It was 8:04 a.m., the start of just another day.

Once on the bus, the man started harassing the passengers. "He was going up and down the aisles pushing and cussing people," Williams' sister said later in the day. "Then he got on Barbara and beat her on the arms and face. He even spit in her face."

Fending off the man with her arms and then turning her back on him, Williams reached into her pocketbook, pulled a pocket knife, turned and stabbed the man once in the chest.

Moments later, the bus stopped in front of 200 Atlantic St. SE. The man, his coat already bloody, stagered out the back door and struggled along the side of the bus toward the front. He collapsed on the sidewalk beside the front door and was declared dead shortly afterward. He was unidentified as of last evening.

The driver called headquarters by radio from his bus and police officers were on the scene within minutes. While detectives detained the bus and its passengers, police arrested Williams. Her face was battered and brusied. Tears stained her cheeks, blood caked her lips.

Later in the day, all charges were dismissed against Williams because prosecutors said there was insufficient basis for charges.

The D.C. Medical Examiner's office said the man died of a stab wound in the heart. Police have sent his fingerprints to the Federal Bureau of Investigation for indentification.

Waiting inside D.C. Superior Court Room 16, Williams' brother Lamont and her two sisters, Mary Williams and Trudy Broome, said they were horrified when their sister called to tell them of the incident.

"She was upset, shaken," said Trudy Broome. "She said, 'I killed someone. He's dead.' She was kind of in shock when I saw her."

Lamont Williams said his sister is single and lives with him and his family in the 4000 block of 9th Street Se.

Shortly after the 3 p.m. interview with her brother and sisters, Williams was released from the D.D. Superior Court lockup after government prosecutors decided to dismiss all charges against her.

According to Williams' attorney, James McComas of the public defender service, the government chose not to prosecute because it was determined that Williams stabbed the man in self-defense.

"We decided there was not a sufficient basis to institute criminal charges at this time," said Assistant U.S. Attorney Henry F. Greene. "The [grand] jury will continue to look into the matter."

As she left the courtroom, Williams was shaken and there was an open gash over her upper lip. She refused to discuss details of the incident and said only that she had never before see the man.

Following a ziz-zag course, the A2 starts its 11-mile course near the Maryland-D.C. line at Southeast Community Hospital on Southern Avenue. From there it carries commuters and shoppers to Wheeler Road, making a series of turns onto Martin Luther King Jr. Avenue, over the 11th Street Bridge, to M Street and eventually onto Pennsylvania Avenue, where it ends at the National Archives at 10th and Pennsylvania NW.

Police said that yesterday's incident was the first fatal stabbing in Metro's history. In June 1974, a Southeast man was fatally shot by a D.C. police officer on a Metrobus when the man quarrelled with the driver over his fare.