With unprecedented speed and little surprise, the Cambridge City Council unanimously elected a mayor at its inaugural Monday morning, as liberal and conservative factions joined forces behind 26-year council veteran Walter J. Sullivan.

Earlier in the day, the eight other city councilors begin their two-year terms after taking the oath of office from the city clerk in a formal City Hall ceremony. Six school committee members also took the oath of office at Cambridge Rindge and Latin High School later Monday afternoon.

The mayor, who was sworn in and began his term immediately after the vote, is a member of the conservative Independent faction of the council. Sullivan became mayor for the third time in his career--50 years to the day after his late father, Michael, took the oath of office as the council's chairman.

The nine-member council also chose longtime member Alfred E. Vellucci as vice mayor. Known as the city's most colorful political figure, the 70-year old Vellucci aligns himself with neither the Independents nor the more progressive coalition of the Cambridge Civic Association (CCA). The 38-year council veteran has been mayor three times and vice-mayor four times.

In his inaugural address, Sullivan said he would work to bolster the public school system and protect "the quality of health care in our city hospital and our neighborhood clinics, which face new threats in the 1980s."

The 62-year old Sullivan told The Crimson Sunday evening that he also would push for reforming the city's rent control and condominium conversion laws in the next two years. But Sullivan, who was last mayor in 1974, said that he would not try to eradicate Cambridge's stringent housing laws.

Since Cambridge adopted rent control 15 years ago, a tenuous balance on the council has preserved the city-wide policy, which is expected to come under attack this term from first-time Councilor William H. Walsh.

Political Intrigue

Choosing a mayor from among Cambridge's nine City Councilors is the first major political battle newly elected local officials face after inaugural every two years. A majority of five votes is required to gain the city's highest office.

Under Cambridge's city manager form of government, the mayor serves as honorary chairman of the council and represents the city at ceremonial functions. The real power as mayor stems from a vote on the seven-member school committee and an operating budget of more than $245,000.

Though balloting for the prestigious council chairman's post has taken up to four months--as in 1948, when Michael Neville was elected after 1321 ballots--behind the scenes jockeying for the job between liberal and conservative councilors generally takes several weeks.

This year, however, all the wheeling and dealing associated with the mayoral selection ended even before city councilors were inaugurated. In a dramatic announcement at the last weekly meeting of 1985, Vellucci announced he would cast the necessary fifth vote to make Sullivan mayor.

"I was leaning against the radiator like I always do [in city council chambers]," Sullivan said yesterday, recalling the announcement. "And Vellucci came up to me at 7:45 p.m. and said, 'Can you get me five votes for vice mayor?"

After immediately calling the two freshman councilors at home and checking with incumbent Thomas W. Danehy, Sullivan said he knew he had the necessary support from the other Independents.

Seven incumbents returned to office as city councilors: Thomas W. Danehy, Francis H. Duehay '55, Saundra Graham, David F. Sullivan Walter J. Sullivan, Alfred E. Vellucci, and Alice K. Wolf. Sheila T. Russell and William H. Walsh are first-term lawmakers.

Three school committee incumbents, Frances H. Cooper. Alfred B. Fantini, and Jane F. Sullivan, returned for their second terms. Sara Garcia, Timothy J. Toomey, Jr., and Larry Weinstein are all first-time school officials