Almas Temple, a half-century-old Masonic structure at 1315 K St. NW, has been declared a historic landmark by the D.C. landmarks commission, blocking a proposal for a $50-million office building on the site.

While the action is not final, it puts a major obstacle in the way of plans by a Philadelphia developer to erect a 10-story building that would occupy the site of the Shriners' temple, an adjacent parking lot and a tire store.

The designation of the structure as a landmark by the D.C. Joint Committee on Landmarks could provide a major test of the city's historic preservation law, regarded as among the strongest in the nation. Announcement of the committee's decision was made over the weekend.

Under the law, landmark status prohibits demolition or exterior renovation of the structure without permission from the landmarks panel or, if appealed, from the mayor's historic preservation officer.

Almas Temple is an ornate and colorful four-story structure with Moorish arches and columns located across K Street from the northern edge of Franklin Park, fashionable in Washington's post-Civil War era but recently the hangout of winos and other street people. With most downtown land west of 15th Street now developed, builders have looked recently for sites to the east, both in and rimming the older downtown area.

Before the committee acted, Rouse & Associates of Philadelphia, which has agreed to buy the Almas Temple site for more than $15 million, applied for a permit to demolish the structure. A hearing on that application will be held tomorrow by the same panel. The development firm is not related to the Rouse Co., a well-known commercial development firm based in Columbia, Md.

The 11-member landmarks commission voted 6 to 3, with two members abstaining, to declare the temple a landmark. The margin was the narrowest possible to take the action, which was done by privately circulating a draft of the final decision and not at a committee meeting.

In its decision, the committee called the temple an "exceptional example of the use of glazed terra cotta," a red pottery-like substance that was commonly used before 1930, and a "successful expression of freedom of design."

Original plans for the office building called for including the facade of Almas Temple as part of the design, as well as providing a new temple in the structure.

Thomas G. McGarry, lawyer for the Rouse development firm, said prospective tenants of the new building have objected to including the colorful tiles because they would give the structure a garish appearance.

While architectural plans for the structure have not been announced, McGarry said those under consideration are imaginative and attractive, and eliminating the Almas Temple site from development would limit the design possibilties.

Previous contested decisions by the landmarks commission have barred the demolitions of the old Bond Building at 14th Street and New York Avenue NW and a former Masonic temple at Ninth and F streets NW.