An Equal Rights Amendment activist is suing four Virginia Democratic groups, claiming she was expelled from the Alexandria City Democratic Committee for helping pro-ERA groups defeat longtime state Del. James M. Thomson.

Marianne W. Fowler filed suit in U.S. District Court in Alexandria yesterday asking for reinstatement as a member and treasurer of the local Democratic committee. She also asks for an order declaring that the Democrats must "refrain from interfering with the privileges and tenure of any [Alexandria committee] member and officer . . . who favors ERA ratification, and who in a non-public way refuses to support candidate opposed to ERA ratification."

The suit, against the Alexandria committee, the Eighth District Democratic Committee, the Virginia Democratic State Central Steering Committee and the Virginia Democratic Party, of which the first three groups are a part, accuses them of violating Fowler's constitutional right to free speech, failing to give her proper hearings after her expulsion, illegal removal from office and breach of contract.

Last Dec. 5, at a bitter meeting marked by hot debate, Fowler was expelled from the Alexandria committee for allegedly violating party bylaws that forbid any committee member from "affirmatively" supporting "by public actions" any candidate opposed by a Democratic nominee.

Fowler was accused of helping defeat Thomson, a staunch opponent of ERA, which has never been approved by the Virginia General Assembly, and of supporting Gary Myers, a pro-ERA Republican who defeated Thomson in the election last November.

In her suit, Fowler asserts that she "at no time . . . affirmatively" supported "by public action a candidate opposed by a Democratic nominee in the Alexandria delegate election."

Fowler is a founder of Virginians for the Equal Rights Amendment (VERA) a group that "decided to commit its resources to oppose James Thomson's reelection," Fowler's suit said. But to avoid publicly supporting the Republican candidate Fowler said she resigned from VERA and joined another pro-Era group "on the condition that (the group) would not engage in any public activity in the Alexandria Virginia delegate race."