The D.C. school board last night gave its approval to a $40 million office development complex on the site of the historic Sumner School building in Northwest. Part of the agreement requires the developers to renovate Sumner for use by the school system.

Under the plan, 17 M Associates, a joint operation of developer Mortimer Zuckerman's Boston Properties firm and a minority firm called First City Properties, will be leased the land adjacent to the Sumner site, a prime quarter-block parcel on M Street between 16th and 17th streets.

In an 80-year lease agreement, 17 M Associates will restore the 110-year-old school building to its original state at an estimated cost of $3 million and construct an office building nearby. The adjacent Magruder School will be reconstructed and used as the entranceway for the new development.

Implementation of the proposal would involve the school system turning the land adjacent to Sumner over to the city, which then would lease the site to 17 M. But before any of that can happen, the District Corporation Counsel must review the proposal, and the project must be approved by Mayor Marion Barry.

The school system plans to use the renovated Sumner building as a research library center that will hold historical artifacts. Space also will be used for school board meetings.