BOSTON--William H. Walsh, a fixture of Cambridge politics for the past decade, is a city councillor no longer.

Associate Justice Neil L. Lynch of the Supreme Judicial Court (SJC) ruled yesterday afternoon that Walsh can no longer serve on the council based on a state statute barring felons sentenced to prison from elected office.

Walsh was indicted on 59 counts of bank fraud and making false statements to the Dime Savings Bank in October of 1992, and was convicted on 41 counts this past March.

Walsh was sentenced to 18 months in prison Tuesday, but remains free pending appeal.

Before the sentence was handed down, Assistant Attorney General Peter Sacks informed all city councillors that, according to a state law, Walsh would have to relinquish his office if sentenced to prison.

Walsh disputed whether the statute was applicable to him.

Sacks sought a preliminary injunction to bar Walsh from the council yesterday morning at a single-justice session of the SJC held before Lynch.

At the hearing, Walsh's attorney James L. Sultan pointed out that the statute calls for the removal of "a convict sentenced...by a court of the United States to a federal penitentiary"

Sultan argued that it has not yet been determined where Walsh will serve his sentence, and his crime was not serious enough to warrant imprisonment in a penitentiary.

He added that removing an official elected by the people was "contrary to the way our democracy works," so it should only be done based on an explicit law.

But Sacks argued, and Lynch agreed, that courts are no longer empowered to determine where sentences are carried out, and that the intent of the statute was to bar officials sentenced to any federal correctional institutions.

Walsh vowed to fight on, both to regain his council seat and to prove his innocence in an appeal.

"I'm going to keep fighting," he said. "If you felt you were guilty, you could just sit there and take it, but that's not the case."

He said there is a possibility that he would seek a ruling before the full SJC on whether he can retain his seat.

"I'll talk to Jamie [Sultan] in the morning," Walsh said.