The City Council is joining the push to get a referendum on the ballot in November that would require the city to cap the number of students in public school classes.

The council speaker, Gifford Miller, who has campaigned on this issue in his bid for the Democratic mayoral nomination, plans to introduce a bill today proposing an amendment to the charter. The Bloomberg administration can, however, prevent a referendum item from getting on the ballot.

In pushing the cause, Mr. Miller is taking on an issue that a group called New Yorkers for Smaller Class Sizes, which is backed by the teachers union and by some parent activists, has been fighting for years.

“Every teacher, every parent, and every principal can tell you that kids can’t learn in a classroom bursting at the seams from overcrowding,” Mr. Miller said in a statement yesterday.

The class-size requirement has only a slim chance of making it onto the ballot. Mr. Bloomberg has already convened a charter commission to study another ballot issue – a move that many said he made to block his opponents from getting another issue on the ballot line.

Further, some education analysts disagree with the position that reducing class size is an effective way to improve student achievement. Some have suggested that creating smaller classes would hinder the city’s ability to find enough qualified teachers. Mr. Bloomberg said the city is already struggling to find enough space to house students because the city has outgrown existing facilities.

“You can’t run the schools through ballot initiatives,” Mr. Bloomberg told reporters yesterday. “That’s just not a great way to govern.”

A spokeswoman for the city’s Law Department, Kate O’Brien Ahlers, said the city clerk was reviewing an existing petition on the issue and would have a decision on it by an August 8 deadline.

“The council proposal is apparently intended to further the petition, and the review of the petition will therefore be relevant to the council proposal as well,” she said.