William Simons, who has been president of the Washington Teachers Union since he led the organization's fight for collective bargaining power in l965, announced yesterday he will seek another two-year term.

Simons, 60, this year faces a serious challenge for the second time in his tenure. For nearly two decades, Simons, a tall, bespectacled man who has long enjoyed a reputation as a fierce fighter for his members' interests, repeatedly won reelection with seeming ease.

He held onto the presidency even though the 1982 election, in which he faced former teacher James D. Ricks, had to be held three times and sorted out in a series of court challenges.

This year, the only other announced candidate in the election that is set for May 20 is Simons' longtime assistant Harold Fisher, 47, who announced his candidacy last month. Simonsof Simons' order because about 100 union members had voted in a meeting to order Simons to reinstate Fisher to his job and to cease all disciplinary actions against him. Simons walked out of that meeting in anger and refused to comply with the order because it was "unconstitutional," he said.

"The membership voted to keep me in my position," Fisher said. "And he has refused to comply with their wishes. It's their union, not his. But he doesn't seem to understand that."

Simons maintains that the firing had nothing to do with Fisher's decision to run against him. The members' motion to rehire Fisher "is an attempt to change the constitution in an unconstitutional manner," Simons said. "The constitution says that the executive board -- not the union membership -- will hire employes under a contract that shall provide due process.

"I did [walk out of the meeting]," Simons said. "The meeting had . . . just broken down into a shouting match and you really cannot conduct business in chaos. We've had a few occasions like this in the past but the work of the union still continues to move."