Six District sites were proposed for designation as landmarks and nomination to the National Register of Historic Places last week at a public hearing before the Joint Committee on Landmarks, a federal-city review board.

If the properties are named local landmarks, they will be subject to District laws governing demolition and alteration of landmarks. And if they are listed on the National Register - a process that might take as long as a year to complete - they will be eligible for tax benefits and preservation grants.

The proposed landmarks are the M Street High School at 128 M St. NW, the elite academic high school for blacks until Dunbar High School opened in 1916; the Northumberland Apartments, an ornate, turn-of-the-century apartment house at 2039 New Hampshire Ave. NW; the Sumner School at 17th and M streets NW, built in 1872 as a school for the children of former slaves, and the Wardman Tower of the Sheraton Park Hotel, 2660 Woodley Rd. NW.

Also proposed for landmark status are two groups of buildings: the east side of the 1000 block of Seventh Street NW, a rwo of 19th century stores once run by German immigrants; and the Schneider Triangle, a late 19th century development of brick rowhouses built by architect T.F. Schneider in the area bordered by Washington Circle, New Hampshire Avenue, 22nd Street and K Street.

The M Street High School, now called the Perry School, was proposed by tha Dunbar High School Alumni Association and Scholarship Fund, which lost a fight two years ago to save the Old Dunbar High School from demolition to make way for an athletic field.

According to Board of Education vice president Carol Schwartz, who testified at the hearing, M Street High School was slated to be torn down to create a playground for students from nearby Terrell Junior High School.

"But on hearing of this application, (by the Dunbar alumni)," Schwartz told the committee, "we went back to the drawing board and found other playground space. The board unanimously supports this application."

The building is currently unused, but Hillyard R. Robinson, an M Street graduate, suggested converting it to a "museum of the historic roots of secondary education for blacks in the nation's capital.

A museum was also mentioned as a possible use for the now vacant Sumner School, which the Board of Eduaction proposed for landmark status. D.C. Council member Hilda Mason suggested that the Norman-style brick school designed by Adolf Cluss be used as a resource center for the D.C. history curriculum being introduced in public schools this year.

Although the school's location is considered prime by real estate devleopers, no one testified against the proposed landmark designation - which would make demolition of the building difficult, if not impossible. Only one application at last week's hearing drew opposition - the proposal by Don't Tear It Down, Inc. to name the 1000 block to Seventh Street NW a landmark.

Raymond R. Ruppert, whose family owns three buildings on the block where they have been in business since 1918, and Jerry Taylor, a representative of the Acme Stove Co., which occupies five buildings on the block, both protested that landmark designation would bring economic hardship to the owners.

When the block was rezoned for apartment houses several years ago in conjunction with an urban renewal plan, said Ruppert, several of the building owners bought adjoining parcels of land, planning to demolish the present buildings and build apartments.

"This property could be put to a higher and better use - especially when the new college comes along," said Taylor. the University of the District of Columbia's downtown campus will be across Seventh Street from the proposed landmark row. Taylor named several other blocks that he called equally significant and more complete than the 1000 block of Seventh Street.

Another area proposed for landmark status by Don't Tear It Down - the Schneider triangle of 22 Queen Anne-style rowhouses near Washington Circle - drew enthusiastic support from several homeowners who attended the hearing. Many of the houses were renovated as luxury residences by developer Marilyn Taylor, who expressed her support of the application so that the houses "will be fully protected for future generations to enjoy."

Among residents of the Northumberland, the City's oldest surviving cooperative apartment building, who appeared in support of their application, was historian and Smithsonian curator James Goode, who had led group tours of distinctive Washington apartment buildings.

"Before the Civil War, apartments were only for poor people," Goode tesified. "The first luxury apartment building in Washington was built in 1879 at 1418 I St. NW."

Goode praised the 69-unit Northumberland, built in 1909 by Harry Wardman, for its Beaux Art exterior and its elegant lobby with an open cast iron and marble staircase.

The Wardman Tower and the arcade that connects it to the main Sheraton Park Hotel was built in 1928 on the site of Wardman's own home - which the builder demolished while his wife was in Europe, according to Floy Brown, who prepared the landmark application on behalf of Advisory Neighborhood Commission 3C.

L. Nord Schweibert, a managing director of the Washington-Sheraton Corporation, testified in support of the application, outlining the corporation's plans to demolish and rebuild the rest of the hotel complex while retaining the tower.