A Washington woman on trial in the murder of her adopted infant son was charged with trying to run down with her car a key government witness in the case outside D.C. Superior Court where the trial was in progress.

Lillie Mae Caldwell Gasaway, 33, was formerly charged on Tuesday after her arrest Friday evening on a charge of assault with intent to kill while armed.

The witness, Margie Malone of the 5900 block of Fourth Street NW, had testified earlier that day on behalf of the government that Gasaway, whom she had known as a friend, was not insane.

Gasaway, the defendant in a two-week-long murder trial in the death of her nine-month-old adopted boy, had pleaded innocent by reason of insanity. The government prosecutor was trying to disprove that contention as a defense in the beating death of the victim.

After closing arguments yesterday by assistant U.S. attorney Richard L. Caplan, Judge Fred B. Ugast ordered the jury sequestered. The jury is scheduled to begin deliberating the murder charge today.

Gasaway had been charged last year with second-degree murder and two counts of cruelty to children after she allegedly beat her adopted son, Hildred Thomas Gasaway, on Sept. 17, 1979. She told police that the boy had fallen down a flight of stairs at home, but the D.C. medical examiner's office said after an autopsy that the victim had died of multiple internal injuries.

The case raised questions about city regulations governing adoptions, as well as the operation of the city's understaffed child abuse office. The office had been counseling Gasaway as a "potential neglect case" for a year before the murder of the boy. Two other adopted infants had been taken from Gasaway by a private adoption agency the summer before the murder.

According to an affidavit, the reported incident involving the car occurred last Friday in front of the main entrance of the Superior Court at Fifth and D streets NW. The affidavit was placed in the court record.

Malone, who was leaving the courthouse after testifying, was crossing D Street when she saw a gray Cutlass driven by Gasaway, heading down Fifth Street.

"She swerved the car in my direction," Malone told a reporter yesterday. "I jumped on the sidewalk. I couldn't believe it. She put on the brakes, she backed up, and appeared to be driving towards the sidewalk," she said.

Malone said she ran into a nearby restaurant where she locked herself in the women's room. Malone told the reporter that she was followed into the restaurant by Gasaway, who was crying and screaming.

Judge Ugast ordered Gasaway held over the weekend at St. Elizabeths Hospital for a determination of her competency to stand trial in the light of the reported incident involving the car.

In closing arguments yesterday, prosecutor Caplan argued that the evidence against Gasaway "is overwhelming."

Gasaway said she "hit him (the victim) at least five or six times in the stomach with all my weight" because he would not stop crying, according to a statement admitted at trial that the defendant had given police.