The Maryland Court of Appeals, in a case that could foreshadow the rewriting of the state's insanity law, today upheld a Howard County judge's finding that a woman who drowned her 5-year-old child was both guilty and insane.

Walking a semantical tightwire over the controversial area of criminal insanity, the state's highest court said guilt and insanity are not mutually inconsistent and that such a finding does not give any greater criminal status to a defendant than the more traditional finding of "not guilty by reason of insanity."

Attorneys familiar with the case said the court appeared to be pushing for "guilty but insane" language to replace the not-guilty-by-reason-of-insanity phrase. The latter is ambiguous in the public's mind, they said, and suggests that a defendant found insane is "innocent" and may go free.

A public outcry for reform of similar statutes arose last year after a jury in the District found John W. Hinckley Jr. not guilty by reason of insanity in his assassination attempt on President Reagan.

In today's ruling, the Court of Appeals upheld the guilty-but-insane finding of Howard County Circuit Judge J. Thomas Nissel in the case of Beverly Ann Pouncey, a 27-year-old Columbia woman charged with first degree murder in the drowning and burning of her 5-year-old son in 1982.

According to court records, Pouncey drowned the child at her home and then burned him on a stove "because she believed the devil was pursuing him and that the only way to prevent him from going to hell was to kill him." Nissel committed Pouncey to Springfield State Hospital, where she must stay until it is determined that she is neither a threat to herself or others.

In handing down the unanimous opinion today, the seven-member court emphasized one of its own rulings from a 1979 case in which it said the purpose of a successful insanity plea is not to establish that the defendant is not guilty but to assure that he is committed to a mental hospital for treatment rather than imprisoned. In its only direct hint that it feels the phrase "not guilty by reason of insanity" is antiquated, the court characterized the term as a "holdover from common law concepts."

A special Task Force to Study the Insanity Defense, headed by Maryland Lt. Gov. J. Joseph Curran Jr., has been watching the courts and is expected to recommend new language to the Maryland General Assembly when it meets next January.

The task force is "still deliberating on the exact language," said staffer Patricia Storch. Lawyers in the attorney general's office said other states have adopted replacement language such as "guilty but not responsible" or "guilty but mentally ill."