Cambridge will have a commissioner at the head of its police department next year if four liberals on the City Council can find a fifth supporter for the City Manager's plan to put a civilian in charge of the city's police.

The four liberals, Councilors Barbara Ackerman, Francis H. Duehay '55, Saundra Graham, and councilor-elect David Clem said last night they will support the establishment of the new office when the new council convenes in January.

A fifth vote in support of the move would make it law.

Speculation about Sullivan's plans for the department began almost immediately after the sudden death of Police Chief Francis A. Pisani November 4.

Pisani's appointment to the top post in the department followed the publication in January of a report by the International Association of Chiefs of Police that termed the city's force "poor" and called for the establishment of a post of "Police Major" to serve under the chief and share the responsibilities of the job.

"Modern Procedure"

Sullivan last month said it was clear the job of police chief "is far too complicated for one man," and last night iterated his belief that the strains of the post "were a major element in Frank Pisani's death."

But Sullivan added he made the decision to recommend that a civilian be placed above the chief rather than ask for a police major because it is a "modern procedure."

Some councilors, however, are willing to let the situation stay as it is, including Mayor Walter J. Sullivan. Sullivan--no relation to the City Manager--said he would vote against "any attempt to put a civilian in charge of the police." Councilor Thomas W. Danehy said he agrees with Mayor Sullivan.

Councilors Leonard J. Russell and Alfred E. Vellucci said they do not know which way they will vote on the establishment of the new post, but both cautioned the council on moving too fast in any direction.

"This is a giant step the city manager is taking," Vellucci said. "It's not something I'm going to let anyone play games with."

Vellucci, an Independent, has been a swing vote on several important issues in the past, casting his ballot with liberals on rent control and in a mayoral election.