A federal appeals court yesterday rebuffed complaints by an Equal Rights Amendment supporter who contends she was illegally expelled as treasurer of the Alexandria City Democratic Committee two years ago.

Marianne W. Fowler, an ERA lobbyist and activist, was ousted by the Alexandria Democratic committee in December 1977 amid charges that she had helped ERA groups in defeating then-delegate James M. Thomson, an Alexandria Democrat who was the Virginia House majority leader. Thomson lost to Gary Myers, a Republican, in the 1977 elections.

Fowler disputed the Alexandria political committee's allegations and filed suit, seeking reinstatement in the committee. At the same time, she ran in the Democratic Party election last June and reagained her membership in the Alexandria Democratic committee.

In a dicision made public yesterday, a three-judge appeals panel in Richmond held that her legal complaints had become moot and ordered her suit returned to U.S. District Court in Alexandria for dismissal.

"We are of the opinion the case is moot. Her reelection to the Alexandria Democratic Committee has granted to her the relief prayed for," the appellate panel said.

Fowler said last night that she had not yet discussed the court ruling with her lawyers and could not comment on it. "I'm certainly not surprised (by the court decision)," she said. Fowler's lawyers could not be reached for comment. Although Fowler was reelected to the Alexandria Democratic committee, she has not regained her position as treasurer.