A D.C. Court of Appeals panel has ruled against developer Dominic F. Antonelli, who sought to raze the Demonet building, a fanciful domed, brick edifice at the corner of Connecticut Avenue, Rhode Island Avenue and M Street NW.

The three-judge panel refused to review a decision that designated the building a historic landmark, thus continuing its protection against being reduced to a heap of rubble.

The building is owned by A&G Limited Partnership, managed by Antonelli, the founder of Parking Management Inc. (PMI). Antonelli wanted to build a high-rise office building on the site, with retail stores at street level. To that end, buildings behind the Demonet building had been knocked down.

The Court of Appeals ruled that it had no jurisdiction to review decisions of the Joint Committee on Landmarks of the National Capital because the committee is not an agency of the District of Columbia. A&G had sought the review under the D.C. Administrative Procedure Act.

"Generally, we're very pleased with the decision," said Karen Gordon, president of Don't Tear It Down. "While it did apply directly to the Demonet building, which maintains the scale on Connecticut and is a really fine building, what it does for the city is to give the Joint Committee a signal to go ahead, and it preserves their effectiveness," she said.

In the fall of 1979, the committee made the building's landmark status official, acting on an application by the Dupont Circle Citizens Association. It was designated a Category 3 landmark, which requires a developer to go through cumbersome processes to seek permission for demolition, with no guarantee of success.

The Joint Committee called the Demonet building "an exuberant example of the rich architecture which characterized post-Civil War Washington." It is the last of what once was a row of Victorian-style houses and was built in 1880 by John Sherman Jr., a local builder.

The Joint Committee spoke of the building's ''unusual octagonal, ribbed dome strongly reminiscent of the dome on Florence Cathedral, its elaborate late-Victorian brickwork, its neoclassical decorative elements and other eclectic details.''

The Joint Committee is an adjunct to the National Capital Planning Commission, with both city and federal representatives.

An attorney for Antonelli said yesterday no decision has been made about whether to appeal.