The Cambridge City Council is considering changing the zoning of the MBTA yard development area southwest of Harvard Square to allow mixed residential, commercial, and office use.

Parts of the yard area are now zoned for residences only, and parts for business only, Ellen Beatrice, an official of the Cambridge Community Development Department said yesterday.

The bill is now on the council table, and if it passes the yard area will be considered a "Planned Unit Development" and the city will have to approve any construction on the site, Beatrice said.

The proposal will probably pass within two weeks, David Carter, chief planner of the Office of State Planning, said yesterday.

Three Cambridge developers have already begun planning their proposals, which they must submit to the MBTA Yards Project Review Board by December 19, according to the "Request for Proposals" which the board issued last Friday. The request issues new guidelines for the developers, whom the Board selected in July from a field of six.

The board will choose one of the developers on the basis of financial feasibility and architectural design, and recommend that Massachusetts Secretary of Administration and Finance Jack Buckley sell the land to him, Carter said.

The entire MBTA yard is to be sold, except for sections planned for the new John F. Kennedy School of Government building, a Kennedy Memorial Park, and a temporary MBTA station, according to the board's requests for proposals.