Cambridge voters went to the polls in moderate numbers yesterday to cast their ballots for nine City Councilors and six School Committee members who will serve two year terms.

Preliminary results indicate that approximately one half of the city's 47,000 registered voters turned out yesterday to choose public officials and decide three referenda questions, election commissioners said after polls closed last night.

In the 1983 municipal election, 66 percent of those eligible exercised their right to vote, mostly because of three heavily debated ballot questions, one of which proposed making Cambrdige a nuclear-free city.

Election commissioners attributed the lower voter turnout to rainy weather and the fact that Cantabrigians were only voting for local offices this year. Most of the other 38 Massachusetts communities holding elections yesterday predicted similar results, except in those cities where mayoral races were hotly contested.

"When you get 51 percent voting in a city election on a rainy day where you don't have a mayoral race, that's not bad," City Manager Robert W. Healy said last night.

Healy, the city's chief executive, said that Cambridge would probably have one of the highest voter turnouts in the state.

The final results of the city council race and referenda balloting will not be available until at least Saturday because of Cambridge's complicated system of proportional representation. Under this system, where voters rank candidates in order of preference, each paper ballot is sorted and counted by hand in a lengthy process that may last up to a week.

Incumbents traditionally fare better than first-time candidates when the weather is bad on election day because they can draw longtime, neighborhood supporters to the polls, former Democratic City Committee Chairman Martin C. Foster said yesterday.

However in 1977, inclement weather proved costly to four city council incumbents and one school committee member who lost their seats when only 23,500 voters cast ballots. Election commissioners estimated last night that 24,374 people voted despite heavy rains and gusting winds.

The impact of yesterday's weather on the next city council's composition may pale in comparison to changing political winds. For city councilors, this election will be "like musical chairs," Foster said. "When the music stops, there are going to be some different Independents sitting in the council when they take the oath in January."

Currently, there are four city councilors backed by the liberal Cambridge Civic Association (CCA), and four loosely affiliated Independents. Incumbent Alfred E. Vellucci, the self-proclaimed swing vote, sides with the CCA on social and housing issues.

Foster predicted that Independent City Councilors Thomas W. Danehy and Alfred W. LaRosa were in danger of being upset by challengers Sheila T. Russell and William J. Walsh, both of whom he said conducted strong campaigns. Candidates need to win one vote more than 10 percent of the electorate, or roughly 2437 ballots, to capture a city council seat.

Porn Backers Cautious

Sponsors of controversial anti-pornography ballot question said yesterday's exceptionally low turnout may spell doom for the proposed ordinance. If passed into law, Question 3 would allow women believing they have been hurt by pornography to sue the makers, distributors, and sellers of such material.

One third of all registered voters in the city must approve the question before the new law could take effect--a figure the referendum's supporters said may be difficult to reach.