A Northwest Washington woman was sentenced in D.C. Superior Court yesterday to 9 to 30 years' imprisonment for the murder of her adopted 9-month-old son and assaults on two more of her four adopted children.

Lillie Mae Caldwell Gasaway was convicted last October of second degree murder in the September 1979 beating death of adopted son Hildred Thomas Gasaway, according to court testimony. She also was convicted of two counts of cruelty to children in connection with assaults on two other adopted children, Varatia, 7, and Nathan, 2. All three children had suffered blows to the stomach, testimony showed.

The circumstances under which Gasaway adopted the children -- still largely unknown by city officials -- prompted Judge Fred B. Ugast to make an unusual appeal during the trial for improved regulations controlling adoptions in the city.

Prosecutors are currently investigating how Gasaway was able to adopt a fourth child while she was awaiting trial on the murder charge.

Under the sentence imposed by Ugast yesterday, Gasaway is to undergo intensive psychiatric therapy. She had pleaded not guilty by reason of insanity at the outset of the trial.

After she was arrested, Gasaway gave police several versions of the incident leading to Hildred's death, including a claim that he had fallen down a flight of stairs. A D.C. Medical Examiner's autopsy showed that the victim had died of multiple internal injuries.