A plan to convert the 83-year-old trolley barn at 14th and East Capitol streets NE into a $10 million housing complex cleared its final hurdle last week when it was approved by the Joint Committee on Landmarks of the National Capital. Zoning changes for the project were approved in December.

Committee members unanimously endorsed architect Guty Martin's proposed renovation scheme for the block-long red brick structure facing East Capitol Street but asked Martin to submit final details for the new Victorian-style houses to be built behind the car barn and to restudy the treatment of the old walls that extend along 14th and 15th Streets.

Approximately 120 housing units-some in the renovated car barn and some in the courtyard behind it-are planned for the site, which covers an entire square block on Capitol Hill. Some of the units may be used as shops and offices, according to developers Robert Hess and Roger Gerstenfeld.

Martin's design calls for gray glass skylights to be placed in the gray slate roof of the car barn to admit light to the upper stories of the houses.

Since there are few entrances to the building alone East Capitol Street, Martin plans to extend some of the window openings and turn them into doors. These alterations to the original structure were opposed by a representative of the Capitol Hill Restoration Society and by Don't Tear It Down Vice President Nancy Schwartz, who said that the skylights and doors "punched holes in the front of the building."

Committee members, however, agreed with Martin that the skylights were necessary to the "adaptive reuse" of the building and that the front doors to be cut in the building were an "urban social requirements."

In other actions, the committee approved a proposal to add four stories to the 17th street side of the Mayflower Hotel, but asked architect Vlastimil Koubek to submit more details on proposed changes in the windows and doors of the building and to restudy the question of the material to be used for the building's cornice.

In the resolution approving the addition, however, the committee warned its sanction of the plan "should not imply any action on the future alteration of the western portion of the building."

According to Koubek, the hotel's owners are studying the possibility of replacing the Connecticut Avenue portion of the hotel with a new office building. A decision by the owners is expected in about a year, according to Koubek.

Under the new landmark law that went into effect earlier this month however, the mayor, on the recommendation of the landmark committee, could refuse to allow the Mayflower's owners to demolish the 54-year-old hotel, which is a landmark.

The landmark law also calls for the committee to review plans for proposed new buildings in the city's historic districts. In the first case under the new law-a proposed office building for the SCI Corporation at 1724 Massachusetts Ave. NW-the committee withheld its approval and asked architect Angelos C.Demetrou to modify his plan in order to make the building more compatible with its neighbors in the Massachusetts Avenue Historic District.

"To borrow an analogy from Star Wars, the proposed building is as compatible with its neighbors as Darth Vader at a lawn party," said committee member Francis Lethridge, an architect, who offered to work with Demetrou to come up with an acceptable design.

The committee also approved five new construction projects in historic districts, some with recommended changes, and declined to approve two other projects. The committee also approved 17 applications for alterations to buildings in historic districts, and turned down one application-for alterations to four houses in the Dupont Circle Historic District.