Following a request by the D.C. School Board, D.C. Superior Court Judge Bruce Mencher yesterday issued a temporary restraining order blocking the demolition of the historic Sumner School.

As wrecking crews stood ready outside the school at 17th and M streets NW, Mencher said that "in the interest of preserving what is obviously an historic landmark," other alternatives to total demolition of the building should be sought.

In granting the 20-day restraining order, Mencher ordered the city's Department of General Services to remove a metal smokestack on the north wall of the building and to tear down a stone retaining wall on the south end of the property.

Mencher also ordered the city to erect barricades around the perimeter of the property until a final decision on the fate of the building is made.

Mencher's order followed a 12-hour order granted by Judge Alfred Burka late Wednesday night.

The Department of General Services had concluded Wednesday that the school, built in 1872 for the children of Washington's freed slaves, was "imminently dangerous and unsafe and should be razed" within 24 hours.

The school had been deteriorating rapidly since it was vacated in June 1978. Heavy rains last week caused the north portion of its roof to collapse, and city engineers say the north and west walls may fall at any time.

At yesterday's hearing, however, an independent structural engineer hired by the School Board testified that the school was safe and could be saved.

The School Board will go to court to seek a permanent injunction when the temporary one expires on Oct. 23.