A woman accused of drowning her 5-year-old son and then burning him on a stove after a D.C. social worker drove the pair home was found guilty of first-degree murder but insane yesterday by a Howard County circuit court.

Judge J. Thomas Nissel sentenced Beverly Ann Pouncey, of Columbia, to 30 days of evaluation by the Maryland Department of Mental Hygiene. After the evaluation, a hearing will be held to determine if Pouncey, 26, should be admitted for treatment in a state mental hospital.

She will be held at Springfield State Hospital where she was sent after her arrest Feb. 28.

Under Maryland law, Pouncey could not have been found not guilty by reason of insanity. Maryland statutes require a guilty or not guilty verdict separate from an insanity decision. Although Pouncey was convicted of murder, the verdict means she will not be held responsible or punished for the act.

Judge Nissel said he regarded Pouncey's actions as a sign that she lacked the "capability to appreciate her conduct" when she drowned her son, William Thomas Pouncey. Nissel also cited a Springfield hospital report that found Pouncey suffering from major depressive episodes with symptoms including psychosis, paranoid delusions and thoughts of suicide.

On the day of the killing, a D.C. social worker drove Pouncey and her son to their home in Columbia around 4 a.m. after both had been seen behaving strangely in a Washington bus station for days and after a decision to separate them had been made by D.C. child protection officials. Within an hour after Pouncey and her son had been returned home, Howard County police found Pouncey's apartment aflame as her dead son, a metal toy truck and newspapers burned on the stove.

After a two-month investigation, the D.C. Office of Inspector General reported it was unable to determine who was responsible for ordering Pouncey and her son to be returned home. The case prompted D.C. officials to initiate stricter procedures for handling emergency child-abuse cases.

Pouncey waived her right to a jury trial and the right to call witnesses. She did not testify yesterday, but repeatedly differed with parts of witnesses' statements, which were read in court, with gestures and comments.

At one point, Pouncey said softly, "I thought the devil was after me and my son. I thought we had to get to heaven and that's all." Pouncey sobbed throughout the trial, particularly when details of her son's death were described.

According to a statement read by her court-appointed lawyer, Daniel Scherr, neighbors of Pouncey said that until 1981 she was "kind, lovable and strongly religious." But toward the end of 1981, Scherr said, neighbors noticed Pouncey had become withdrawn, paranoid and began to wear provocative clothing after her son had come to live with her.

Neighbors also reported to Scherr that Pouncey began hallucinating, became paranoid when people hugged her son and thought her friends were trying to "trick" her into bearing another child.

Her lawyer cited a police statement in which Pouncey reportedly said after her arrest that the baby's father made her kill the child--that her ex-husband was inside her body. Police said Pouncey said, "Evil forces made me kill my son."

A neighbor of Pouncey's told the court that once while visiting Pouncey she "heard her arguing with a man in another room." When the neighbor went into the room to check on the disturbance, Pouncey was the only person there.

James Dudley, the special state prosecutor for the case, read a statement from employes of the Trailways bus station, where Pouncey and her son were found wandering, that said Pouncey had tried to stuff a handful of blue sleeping pills into her son's mouth. Police said Pouncey also had taken sleeping pills. Dudley said Pouncey continuously repeated throughout that night, "Jesus is coming . . . oh God let me die," uttering growls and rolling her eyes back in her head.

Much of the five-hour trial was devoted to arguments over whether Pouncey should be found guilty of two other charges related to the killing. Pouncey also was charged with manslaughter and arson, but Judge Nissel said that the manslaughter charge was eliminated with the murder conviction. Nissel found Pouncey not guilty of arson.