The exit of two incumbents from the 1989 City Council election has led possible candidates to begin jockeying for support more than a year in advance.

Last week, City Councillors David E. Sullivan and Saundra M. Graham announced they would not seek re-election next year. Both are members of the pro-rent control Cambridge Civic Association (CCA), and their withdrawal could leave the Council open for a possible shift in its balance of power.

For the past four years, the same nine members have been all but stalemated. There have been four CCA members, four more conservative, neighborhood-oriented Independents, and Alfred E. Vellucci--now the Mayor--who votes with the CCA on housing policy and with the Independents on many other issues.

Several political observers said many candidates were frustrated by the 1987 election results, which left all nine incumbents seated.

Observers say a shift from this pattern could pave the way for a change in the city's rent control policies.

"Prime contenders" for the open seats include CCA member Jonathan Myers and Edward N. Cyr, according to City Councillor Sheila T. Russell who, like them, lives in North Cambridge.

Although Cyr ran as an Independent in last year's election, he said he supports many of the CCA's goals. In that election, Myers and Cyr came in 10th and 12th, respectively, in a race for nine seats.

Russell said last night she "had a feeling" the candidates are already trying to gather support for next year's election, adding there was much speculation on who will take Sullivan and Graham's seats. If unknown candidates were to gain the seats, she said, they are likely to be different from current Councillors--"a little more conservative than the liberal CCA, [but] not the old guard."

However, Russell said, "anyone new would have to be a real flash--someone who gathered a lot of publicity fast."

Asked about possible candidates to replace Graham and Sullivan, Vellucci said he "could care less who's running."

"I could care less if David Sullivan or Saundra Graham comes or goes, the City of Cambridge will go on," he said.

"You'll see some candidates come out of the woodwork," said Myers. "There's been a lot of speculation about it."

Myers also called the vacancies "slightly enticing," and said the city was "ripe for a swing in this political direction," referring to the CCA.

Cyr, who has said he will probably run for Council, said last night that he was surprised so few candidates had announced they will run next year.

"I can't figure out what it means," added Cyr. "I haven't seen two open seats in my lifetime." Cyr said he was sure there would be a "larger field" by election time.

Both Cyr and Sullivan said last night that there had been some discussion of the CCA possibly taking a fifth seat on the City Council, thus bumping an incumbent Independent. Both also said a fifth seat was possible in 1987, and Myers staked his candidacy on that possibility last year.

But Sullivan added, "My guess is that this won't happen," saying he thought the "balance on the Council will remain the same."

"If David and Saundra are not running, it increases the field of strong pro-rent control candidates substantially," said Cyr. With so many of these candidates running, he said, the CCA could "take an Independent seat" because people who previously supported Sullivan and Graham would now be free to vote for any one of the liberal candidates--whose vote totals might thus outnumber that of an incumbent Independent.

Referring to the city's proportional representation voting system, Cyr added that the "battle is at the end of the ballot" where candidates often gain or lose the last few seats by a comparatively small margin of votes.

Since City Councillor Thomas W. Danehy had the fewest votes among the Independents in the last Council election, he might be the "weak candidate" in next year's race, said Esther M. Hanig, chairman of the Democratic City Committee. Cyr agreed, saying "some of the weaker candidates could have real problems."

Like Sullivan, Hanig said she did not think next year's election would "change the rent control configuration" in the Council. Asked if she might run for City Council next year, Hanig answered, "I don't think anyone active in city government isn't thinking about it."