The Washington chapter of the liberal Americans for Democratic Action has criticized as "a blatant power play" D.C. Del. Walter E. Fauntroy's efforts to discourage City Council member Marion Barry from running for mayor.

Barry has been under increasing pressure from Fauntroy and other leading city Democrats to run for Council chairman instead and not challenge the current Council chairman. Sterling Tucker, whom Fauntroy and others favor for mayor.

Open of the arguments being made by Fauntroy, according to well placed party sources, is that Tucker is older, more experienced and has served a term as Council chairman, while barry has not.

In an Oct. 12 letter to Fauntroy, ADA Chairman John Issacs wrote, "The politics of a limited choice by a few political brokers who take it upon themselves to decide who has served enough time to run for higher office and who has not is an unhealthy trend in District Democratic politics."

Fauntroy declined comment on the letter.

The ADA letter asserted that if Barry were not in the race, District Democrats - one of every three registered city voters - would have to choose basically between Tucker and Mayor Walter E. Washington (neither of whom his formall announced their candidacy.

That would be unacceptable," he wrote. "Walter Washington has proved himself to ba a very incompetent mayor and his administration had been lacking in imagination in dealing with the city's problems." Issacs said in an interview yesterday. "Sterling Tucker shows more promise, but he seems to bs fairly conservative and pretty well tied into the business community."

Issacs said the local ADA chapter, which endorsed Clifford Alexander in the 1974 mayoral race, has not decided whom it will back next year. "There is more of a feeling for Marion Barry, but there's no commitment to him," Issacs said.

The letter said that twice in the past, similar efforts were made by Fauntroy and others "to limit the electoral choice for Washingtonians." This was a reference to the 1972 and 1976 presidential primaries when Fauntroy ran as a "favorite son" and urged D.C. voters to vote for him rather than one of the announced presidential candidates.