By ans rime next week. Cambridge will have a new City Councilor maybe a new mayor and most certainty the start of the most unpredictable political face it recent memory.

While the death of Mayor Leonard J. Russell on June 16 has prompted speculation about who will move in to the race for his City Hall seat, it has also led the Cambridge School Committee to postpone its meeting until Russell's seat is filled.

Unlike cities where mayors are popularly elected, Cambridge's mayor is elected every two years from among the ranks of the nine-member city council Russell's vacant council seat must be filled before the entire group can select the next mayor.

To start the process, the Elections Commission will meet this Tuesday to recount the 2099 ballots Russell, a five-term city councilor, won in the last election. Under Cambridge's complicated system of proportional representation, a successor will be chosen from among the seven candidates for city council who failed to gain a seat in 1983.

Political observes are saying that Alfred W. LaRosa, a resident of East Cambridge who ran as an Independent, will gain the ninth City Council sent once all of Russell's ballots are redistributed among the eligible candidates.

"The conventional wisdom holds that LaRosa will finish first, Richard P. Branson second, and David A. Wylie will end up third," said one local politician.

LaRosa, whose neighborhood-oriented, conservative constituency is considered closely allied to Russell's gained roughly 1100 ballots in 1983.

The process of selecting a new mayor of Cambridge will not begin before the full city council convenes on July 8.

Political Jockeying

Meanwhile, in a politically charged move last week, the Cambridge School Committee voted to cancel all its regular summer meetings until the city council fills its ranks and can choose a new mayor.

A Cambridge mayor serves as the chairman of both the nine-member city council and the seven-person School Committee.

Four school committee members, led by Glenn S. Koocher '71, said they would not recognize the leadership of the interim mayor, Francis H. Duehay '55.

"We want to give the City Council a chance, to meet in full complement and elect a mayor." Koocher said this week. "No substantive argument can be made for the vice chair of the City Council sitting on the School Committee."

Although Koocher argued that such a move is unprecedented in the history of Massachusetts school boards. Cambridge City Solicitor Russell B. Higley said this week that sitting on the School Committee was part of Duehay's duty as view mayor and acting chair of the city council.

"The School Committee should do business as usual and the will of the city charter should be carried out," said Duehay, who added that he "won't start hurling accusation toward school committee members" in this volatile breuhaha.