Federal authorities said yesterday that results might be available by the middle of the week from their investigation into Friday night's suspicious fire that severely damaged the offices here of the American-Arab Anti-Discrimination Committee (ADC).

The blaze at 1731 Connecticut Ave. NW caused about $500,000 in damage to offices in that building and to an adjacent grocery store. It is under investigation by the Bureau of Alcohol, Tobacco and Firearms, a branch of the Treasury Department.

In addition, FBI Director William Webster said yesterday on ABC News' "This Week with David Brinkley" that his agency will enter the investigation "if there's any indication of a terrorist activity."

James G. Abourezk, national chairman of the ADC and a former Democratic senator from South Dakota, has called the fire an effort to suppress ADC's views.

"This is the third serious attempt to stifle the political dissent that comes from the American-Arab Anti-Discrimination Committee," he said Saturday at a news conference outside the scene of the spectacular two-alarm blaze.

A bomb planted at the ADC's Santa Ana, Calif., office killed the group's West Coast regional director Oct. 11. On Aug. 16, a police officer was injured when a bomb exploded outside the ADC's office in Boston.

Webster said on the television show that the FBI is following the incidents "very closely."

Investigators searching for the cause of Friday's fire here found indications that someone had ransacked offices of a second-floor public relations firm below the ADC offices, which are on the third and fourth floors, according to an official familiar with the investigation.

According to the official, the investigators said file cabinets and drawers in the public relations firm were opened and material was strewn about.

In addition, this source said, the first firefighters to reach the scene of the fire thought they smelled an accelerant, a chemical that could be used to hasten the spread of a blaze.