After two years of battles between a downtown developer and historic preservationists, the District government yesterday cleared the way for the demolition of Historic Rhodes Tavern, the city's oldest commercial building.

A District official granted a demolition permit to the Oliver T. Carr Co. to clear the tavern site at 15th and F streets NW for a $60 million, 12-story office building.

The only remaining avenue for the building's supporters is an appeal to the D.C. Court of Appeals.

The 180-year-old tavern, the birthplace of the Riggs National Bank and the National Press Club, was the dining spot of British soldiers who watched the White House burn in 1814 from the tavern's third-story windows. The building, listed in the National Register of Historic Places in 1969, now houses a newstand, a restruant and several other shops.

The city's decision to allow the demolition of the tavern marked the first time the "special merit" clause of the city's 1978 historic preservation law was invoked. The law generally makes it more difficult to tear down historic buildings, but the "special merit" clause allows such buildings to be demolished when the new structure will feature "exemplary architecture" or serve the community better.

The Carr company, with the support of the city planning department, argued that the architecture of the new building would "exemplary" and the three-story tavern could not be incorporated in the design because of its height.

Carol Thompson, the mayor's agent, or arbiter of such preservation decisions, rendered her verdict yesterday following three days of hearing in December in which both sides marshaled dozens of experts to testify. Thompson took the maximum amount of time -- 120 days -- from when she received the application in October to announce her findings.

Yesterday's decision could affect the outcome of hearings later this month on the 70-year-old Elks Club, located on the site of the District's new convention center development six blocks away.

Preservation groups will challenge the city planning department's approval of a demolition permit for the site; the city government will argue that the convention center is also a "special merit" case.

Joe Grano, co-chairman of the Citizen's Committee to Save Rhodes Tavern, said Thompson's decision was "a disgrace." He said his group would appeal it to the court.

As part of the project on the tavern's block, Carr will incorporate two other historic facades, the Keith-Albee Building, at the corner of 15th and G streets NW and the National Metropolitan Bank Building, 613 15th St. NW, as well as the interior of the Old Ebbitt Grill at 1427 F St. NW.

Thompson said that his project was "exemplary" because of the "sensitive incorporation" of the old buildings' facades.

"The facades . . . create a major design impact at one of the most strategic locations along the ceremonial route between the Capitol and the White House," Thompson said in her decision. ". . . These facades offer particular reinforcement to the monmentality and powerful rhythm of the colonnaded east side of the U.S. Tresury Building."

Under present plans, the building will not be torn down until Jan. 1, 1981, at the earliest.

In December Carr signed an agreement with another preservation group, the Committee to Preserve Rhodes Tavern and the National Processional Route, in which he said he would not tear the building down until that date. The group hopes to raise the funds to move the building to another site on Pennsylvania Avenue -- as yet undetermined.