D.C. City Council Chairman Sterling Tucker thought it was a chance for the decisive boost to victory in his extraordinarily tight battle with Mayor Walter E. Washington for the city's Democratic mayoral nomination.

The tantalizing prospect dangling before him was that the third candidate in Tuesday's primary, City Council member Marion Barry, might withdraw and endorse Tucker.

Instead, it turned out to be an election caper engineered by Barry's forces.

Tucker went to a scheduled meeting late Thursday night at which he expected to talk to Barry about ways the two of them could join forces, including Barry's possible withdrawal, in order to defeat the mayor.

But Barry, who at one point. Thursday had agreed to attend the political summit at the home of the Rev. David Eaton, never showed. Barry said yesterday he never had any intention of discussing a withdrawal from the highly contested race.

"It might have been naive of me," Tucker said, "but I thought he would show up. He said he would."

But Barry's campaign manager, Ivanhoe Donaldson, said Barry never had any intention of attending the meeting. Donaldson said Barry had agreed to it earlier Thursday only as a ploy to forestall the anticipated endorsement of Tucker by Eaton and the politically influential Ward 3 council member, Polly Shackleton.

The Tucker campaign had scheduled a press conference for 3 p.m. Thursday in which Shackleton, Eaton, golfer Lee Elder and the Rev. William Wendt were to endorse Tucker. The Tucker camp billed it as the turning point of the campaign. But when reporters showed up, they were told mysteriously that no announcement would be made on Thursday but that they should be prepared for news the next day.

What was going on, both Barry and Tucker forces acknowledged yesterday, was a series of telephone calls between the two camps, with the Barry forces dangling before Eaton and Tucker partisans the possibility that Barry might consider withdrawing from the race if both sides could get together at a late night meeting at Eaton's house.

"The strategy on my part was to keep David (Eaton) thinking and play for time," Donaldson said.

The bizarre incident was the latest chapter in the increasingly bitter election campaign in which Tucker and his advisers have attempted to convince voters and public officials that vote for Barry will only help to relect Mayor Washington for another four-year term.

A Washington Post poll last Sunday showed Tucker and the mayor in a virtual dead heat, each with about 31 percent, and Barry trailing with 24 percent.

As a result, Tucker forces all week have attempted to portray the election as a two-way race between Tucker and Washington and that Barry has no practical chance of winning. Tucker campaign workers have mailed 5,000 fliers with the Post poll results to undecided voters in the city where Barry is strongest - focusing on Shackleton's Ward 3 - hoping that voters will be convinced that Tucker is the only candidate at this point who can beat the mayor. Barry, on the other hand, has attempted to hang on to his support.

Tucker strategists are banking on the theory that many voters can accept either Barry or Tucker as mayor and most of all want to defeat Walter Washington.

Throughout the campaign, Tucker's most prominent political mentor, D.C. Del. Walter E. Fauntroy, has voiced the fear that a "divided majority" supporting Barry and Tucker will give the election to Washington by sharply splitting its vote.

Yesterday, a day after the originally scheduled press conference, Shackleton did endorse Tucker, and Eaton, Elder and Wendt did also.

Shackleton said she endorsed Tucker because she had "come to the viewpoint because that if the vote is split between two candidates, Mayor Washington may well win." Throughout the campaign, she has said that either Barry or Tucker would be acceptable to her as mayor, but not Washington.

Shackleton immediately made a radio advertisement for Tucker's campaign. But when she was asked if she plans to urge her constituents in Ward 3 to vote for Tucker, she said that she will only ask voters "to examine their own consciences and vote accordingly."

Tucker said he agreed to the late Thursday meeting with Barry and to the Thursday press conference postponement so that he could "explore every possibility" of forming some kind of coalition to defeat the mayor.

"I was prepared to have a full-range of discussions," Tucker said, adding that he had "nothing specific in mind" to offer Barry in a Tucker administration.

Tucker "could have decided right then (at the meeting) that he would name Barry city administrator" or to some other high position in his administration, Eaton said.

Tucker declined direct comment on the Barry camp's tactic to thwart the meeting, but said, "That should say something about them."

Tucker, accompanied by two of his chief strategists, Robert B. Washington Jr. and Harley J. Daniels, showed up at Eaton's northwest Washington home at 11:35 p.m., Eaton said, and the four of them waited for Barry.

But 20 minutes later, Herbert O. Reid, a Howard University law professor and close Barry adviser, called and said Barry would not be coming to the meeting because news of the impending endorsement by Shackleton, Eaton and the others had been leaked to the media. Some radio stations even carried stories on Thursday saying Shackleton, had endorsed Tucker.

Yesterday Barry, at a press conference in front of his campaign headquarters, was at odds, not only with the account by Tucker and Eaton but in sharp conflict with the version given by Barry's own campaign manager Donaldson.

Barry told the press conference he had agreed to the meeting with Tucker at Eaton's house as a means of persuading Eaton not to endorse Tucker.

"I am confident I can win," Barry said. "Even if I were not confident, I would not drop out because we've established some principles in this campaign.

"Why are they (Tucker supporters) ganging up on Marion Barry if he can't win?" Barry asked. "I'm not panicky as Sterling Tucker is. Stering Tucker's campaign is in disarray."

Despite having sought Shackleton's endorsement himself, Barry said he thought the impact of her support for Tucker "will be minimal."

Later, Barry supporters said they thought that by delaying the Shackleton endorsement for one day they had taken some of the edge off her announcement of support for Tucker.

Among the city's eight wards, Barry is strongest in Ward 3, the politically potent, largely white, affluent election district west of Rock Creek Park. When Shackleton's impending endorsement of Tucker became known in the city's political community early Thursday, many of her supporters who are backing Barry in the mayoral campaign immediately called her to protest.

The protest, as it turned out, had been organized by Barry campaign staff workers.