A split panel of the D.C. Court of Appeals in a rare move ruled yesterday that a large addition under construction at the George Washington University Medical School was improperly approved by the city's zoning board.

Although the panel reversed the board's decision and ordered it to reconsider the facts in the case, lawyers said yesterday it was unclear if the panel decision would halt construction of the eight-story addition.

The addition under construction at the rear of the H.B. Burns Building, stretches along 22nd Street to I Street NW. A lawyer for the university said the foundation for the addition already had been laid and the floors poured.

In their 27-page opinion, the panel ruled 2 to 1 that the board failed to consider how the addition would affect traffic and the light and air available for neighborhood residents. The panel also found that the board erred when it ruled that the university was not required to apply for a special zoning variance.

James T. Draude, who lives in a neighboring condominium, had argued in his appeal of the zoning decision that the addition would tower 35 feet above the west wall of his building and would block light and air now coming into the condominiums. He also argued that the addition would increase traffic congestion in the area.