D.C. City Council Chairman David A. Clarke ended months of speculation about his political future yesterday, announcing that he will seek reelection to his current post and not challenge Mayor Marion Barry for the mayor's seat this fall.

Clarke, who is completing his first term as chairman, said he believed that he could beat Barry but only if he were the only major opponent in the race. "I took a poll and the poll showed that it would be possible to go one on one [against Barry] but that if there were more than one major opponent in the race, the tendency would be for the opposition to split," ensuring Barry's reelection, he said. He added there was no guarantee that another council member or another contender would not enter the race.

Meanwhile, City Council members and Barry's campaign chairman said yesterday that Clarke's decision to seek another four years as chairman was no surprise in view of Barry's perceived strength among the electorate.

Clarke's announcement "is a bit of nonnews," said John Hechinger, the Democratic national committeeman. "I believe that Chairman Clarke will win going away if anyone even dares to challenge him. I likewise believe Mayor Barry will probably have very little competition other than that which has already" announced for mayor.

"I never expected [that Clarke would] do anything else," said council member Frank Smith (D-Ward 1). "I think that by now the public ought to be used to people who titillate, tantalize and play games with them."

In addition to Clarke, who said early in the year he was considering a challenge to Barry, council members John A. Wilson (D-Ward 2) and Charlene Drew Jarvis (D-Ward 4) have been weighing a bid for the seat. However, two weeks ago Wilson said he "probably" would not run. Jarvis has said she was waiting to see how the political races developed. Neither could be reached yesterday for comment.

Barry said last week it was "not a question of if, but when" he would announce his reelection campaign. So far, four candidates have formally announced: former school board member Mattie Taylor, health care consultant Brian Moore, sex entrepreneur Dennis Sobin and unemployed accountant Calvin Gurley.

Clarke announced his intentions in a statement released late yesterday, after a meeting with his wife Carole and their 11-year-old son.

The council chairman, noting that a losing bid for mayor would put him out of elective office, said he preferred to remain as chairman and continue his efforts to keep the legislative body an "independent and coequal branch of the District of Columbia government."

"I just had to make the decision as to whether being an opponent was worth giving up being the watchdog," he said, referring to what he called "constructive tension" between the council and the mayor.

Clarke appeared confident of his reelection chances, citing results of a poll of more than 600 residents citywide that he commissioned early this month. "I feel very comfortable," he said.

Council members Polly Shackleton (D-Ward 3) and Smith said they believe Clarke will be the front-runner if any opposition develops for the chairman's seat. Jarvis has been mentioned as a possible challenger.

"Dave as the incumbent would have to be perceived as the front-runner, but I think it remains to be seen how much damage has been done by waiting so long to marshal his forces," Smith said.

Wilson and others have said Clarke's hesitation in making a decision had effectively blocked the entry of Wilson into the mayor's race. Clarke, however, denied he had made any deal with Barry to prevent others from challenging the mayor, and Shackleton dismissed the notion as political chitchat.

Max N. Berry, Barry's campaign chairman, said he thought Clarke's move was a "wise decision" but said it made little difference to the Barry campaign.

"Had he run it would have made it a little more exciting to us," he said. "His political instincts told him he would lose and lose badly, and if he did lose it would ruin his political future in the city."

James Christian, chairman of the D.C. Democratic State Committee, said a week ago he believed that Clarke and other potential mayoral challengers would wait until 1990 to run for mayor, and Clarke hinted yesterday he might feel differently then.

"In 1990, I will have served as chairman, I hope, for eight years instead of four, and my personal attitude about remaining chairman might be different at that time," he said. "However, I am not doing this running for reelection as part of a strategy."