A D.C. Superior Court judge has sentenced a Long Island lawyer to a suspended 90-day jail term and a $300 fine for illegally arranging the adoption of a baby born here last Oct. 18.

Edward Galison, 37, was arrested outside George Washington University Hospital Oct. 23 with the child in his arms. He had just paid more than $2,200 to the baby's grandmother for delivery to its 19-year-old mother in behalf of a New York couple who wished to adopt the child.

Judge William C. Pryor, who handed down the sentence Monday, issued a written opinion last Feb. 16 in which he found Galison guilty of violating a 36-year-old D.C. statute that makes it a misdemeanor for unlicensed persons to act as intermediaries in adoptions.

Assistant D.C. Corporation Counsel Larry McClafferty said Galison was only the fourth person prosecuted under the statute since it became law. He said the last previous case occured in 1963.

McClafferty said prosecutors asked Judge Pryor to give a prison term to Galison to deter others. He said that beceause of birth control, abortions, and a willingness on the part of many unwed mothers to keep their children, the number of babies available for adoption is declining.

Leslie Scherr, Galison's attorney, said Galison told Pryor that he was unaware that his actions here were a violation of D.C. law. He said they were legal in New York.