The Massachusetts Senate passed a bill on Monday that would allow a referendum on proportional representation to appear on the Cambridge election ballot this fall. The vote was 9-4.

The bill will now go to the State House, where action is expected within a week or two. If the bill receives both House approval and is signed by the Governor, Cambridge citizens will be permitted to file a petition to put the PR referendum before the public in November.

At present, Cambridge is the only major city in the United States which uses the PR system in its elections. Proposals to abolish the system have been defeated four times since it was first used in the city in 1942. The last defeat came in 1961, when voters retained the system by a margin of only 455 votes.

Under present state law, referendums about election procedure can be introduced only once every four years. If the new bill doesn't receive final approval, therefore, a PR referendum cannot appear on the ballot until 1965. Opponents of PR have favored the bill. They apparently believe they have a better chance of defeating the system in a year with a state election.