A Cambridge citizen action group attempting to stall construction on the Observatory Hill athletic complex will request today that the city purchase the proposed building site from Harvard.

In a letter that will be submitted to the Cambridge City Council the Quality of Life Committee of the Peabody School Council will also request that the council consider long-range plans for preventing future Harvard expansion in Cambridge.

Radcliffe cannot obtain a building permit for the complex until the council votes on a down-zoning petition submitted last month.