Legislation to authorize Massachusetts to buy the Bennett Street transit yards the site for the John F. Kennedy Memorial Library was introduced into the General Court (state legislature) yesterday.

Under the bill, the state could cede as many as 11 of the Yard's 12 acres to the feral government, which will run the Library. The state could sell to the Library Corporation the remaining one acre and any other land that is unneeded for the actual construction of the Kennedy Memorial.

The Corporation, in turn, could dispose of this land as it sees fit. Around two acres are expected to be given to Harvard for the construction of an institute of Politics, which will be associated with the Library.

Sen. James Burke (D-Brockton), the bill's sponsor, estimated it would take about thirty days for the legislation to gain the approval of both houses and reach the governor's desk. A public hearing before the Joint Committee on State Administration will probably be held next Wednesday or Thursday, he said.

The Bennett St. Yards, across Boylston St. from Kirkland and Eliot Houses, are owned by the Massachusetts Bay Transit Authority. The state would pay the M.B.T.A. about $6 million for the land.

The new legislation seems to allow I.M. Pei, the Library's architect, the flexibility he has repeatedly asked for. Pei has said that he would like to include "supporting facilities"--parking lots, restaurants, shops--on the Bennett St. site near the Library. The bill would permit the Library Corporation to sell part of the Yards for the development of such facilities.

Burke said, however, that he expected that all but the two acres needed by the Institute of Politics would be retained by the federal government. Any parking or eating establishments could be supported on the government land, he declared.

A source close to Library said that any conflict over how the supporting facilities ought to be run would probably be worked out after the legislation is passed. It will be about two years before the M.B.T.A. can leave the Yards', he noted, and this should be enough time to iron out details.