Michael Reed, 20, convicted of mayhem and other charges in a sledgehammer assault last April on a 19-year-old youth, was sentenced to prison yesterday by a judge who said the defendant's criminal record was one of the "grossest" he had ever read.

D. C. Superior Court Judge Eugene Hamilton sentenced Reed to 10 to 30 years for armed robbery in the case, 15 to 45 years for assault with intent to kill and five years for mayhem, the sentences to run consecutively.

court officials said that Reed would not be eligible for parole for at least 18 years.

The victim of the assault was Carlos Gomez, a promising artist, who suffered massive skull and facial injuries in the assault at 10 p.m. April 24 in the rear of the 1300 block of Brentwood Rd. NE. His mother, Carol Gomez, said her son was blinded in one eye and doctors have warned that his recovery from a multitude of injuries is not complete.

"He (Reed) should be out of the way for a while," Assistant U.S. Attorney Michael Pace said. Pace suggested to Hamilton that Reed should be sentenced as though his victim had died, and "not be rewarded because of the skill and dedication of the surgeons" who saved Gomez's life.

Court records show that before Reed forced Gomez behind a restaurant and hit him on the head 10 times with a 5-pound sledehammer that he had been arrested 37 times since 1968.

"(Reed) has had every conceivable type of rehabilitation known to man." Hamilton said before imposing sentence. Nothing, the judge observed, had changed him.