Some long-anticipated play-forkeeps politicking for the Democratic nomination for mayor got under way yesterday, as all three of the major candidates and their surrogates plunged into the final and decisive 12 days of the campaign.

Stand-ins for City Council Chairman Sterling Tucker launched radio ads and made verbal denunciations of Council member Marion Barry, who Tucker supporters believe is taking away many of their candidate's votes.

Barry, claiming he has gained new momentum from a newspaper endorsement, released a 192-page tax reform "project report," ostensibly aimed at reinforcing his contention that he has done the most for city taxpayers.

Mayor Walter E. Washington had plans to hold a 'victory party' last night in the high voting North Portal Estates section of upper Northwest Washington. At his headquarters, campaign workers were already stuffing packages to be mailed out to poll watchers for use on election day.

"There's more support for the mayor than a lot of people realized and people are just coming around," said an optimistic Warren Graves, director, of field operations for the Washington campaign. "I think Tucker is fading. But he is still the principal opposition because Marion Barry is not going to win."

For months, the candidates have each gone through see-saw schedules of activities, giving out position papers, analyzing polls, holding press conferences, attending forums and combing city neighborhoods in an effort to identify their potential supporters.

Now, the all important two phase level of the final days has begun. The candidates themselves are expected to sharpen their verbal attacks on one another and draw more precise lines of political battle. At the same time, campaign workers will begin hitting the streets en masse this weekend in a last-ditch effort to shore up political support.

"We're in the last lap," declared chief Tucker campaign strategist Robert B. Washington Jr., as volunteers hauled out boxes of "Tucker Mayor. Now" signs to be plasted on posts, and receptionists' fingers went from button to button as the telephone line kept lighting up.

The principal target of most of yesterday's political rhetoric was Barry, who Tucker's organization claims is a "spoiler" in the race - a candidate too fare behind to win, but capable of drawing from Tucker enough votes to catapult Washington to victory in the essentially three-way race.

Standing in front of the rundown buildings of the Lincoln Heights housing project in far Northeast, council member Willie J. Hardy (D-ward 7), a supporter of Tucker, called Barry " a loser" and urged those who form the coreof Barry's political base - affluent whites and women - to change their minds.

There are people, Hardy said, "who honestly believe Marion Barry represents the blacks of this city. My answer to that is: as a flamboyant politician, Marion may be entertaining. But that won't cut it as mayor."

"I want the white women in Ward 3 to understand," Hardy said. "I want them to know how these people out here in my ward feel."

Hardy, surrounded by tenants on 50th Street NE, said Mayor Washington had defaulted on promises he made four years ago to repair the projects. As a result, she claimed, many tenants had to endure bitterly cold winters without heat and hot water.

To vote for Barry would be to vote for Washington's continuation in office, she said. "Mayor Washington always says he is doing the best he can. His best has kept my constituents cold and with no hot water," said Hardy.

(City housing officials said there are plans to repair the projects soon.)

Hardy's theme was echoed by D.C. Del. Walter E. Fauntory, who is unopposed for renomination in the Sept. 12 primary, but is spending about $10,000 for advertising that links his shoo-in candidacy with that of Tucker and council member Arlington Dixon, who is seeking the nimination for council chairman.

Barry, who has been a self-described underdog in the campaign, has been buoyed the past few days by the endorsement of his candidacy Wednesday in an editorial in The Washington Post.

"He no longer has to be aggressive in seeking people," said campaign press coordinator Florence Tate. "People are now coming to him. We've had lots more calls from people who want to schedule events, coffees and fund-raisers for him."

Like most of the candidates, Barry has been concentrating on undecided voters, who have been considered the decisive swing vote in an anticipated close election. He now makes about 10 to 30 calls a day at the 25-unit telephone bank on the third floor of his campaign headquarters, trying to persuade undecideds to join his camp.

Barry said yesterday that assertions by Tucker strategist Robert Washington that the Barry candidacy is fading (missed the mark. "What do you expect Bob Washington to say," Barry said. "I'm building. I'm not as far behind as when I started."

Washington, is expecting many of the independent efforts being run on his behalf to jell in the final push toward election day.