Sterling Tucker stood alone anxiously craning first one way and then another, as he tried to get a clear view of Marion Barry, the Democratic nominee for mayor, who was at the microphone.

Tucker, chairman of the D.C. City Council and the second-place finisher in last month's close party primary for mayor, had left the microphone moments earlier. He had shaken hands with Barry and raised his glass in honor of the man who defeated him.

"Let's have a big toast for a united Democratic effort to Nov. 7," an elated Barry had said. And the hundreds of people in the chic three-tiered foyer of the Mazza Gallerie shopping center on Friday night toasted, applauded and shouted their approval.

But now, as Barry introduced the "team" of Democratic nominees for the Nov. 7 general election, Tucker was conspicuously out of the spotlight, even though he is one of the four major Democratic politicians in the city and was an honored guest at this $50-a-person "We're Coming Together" dance Friday night.

The other two would be honored guests were not present. Mayor Walter E. Washington, Barry's other rival in the primary, was home recovering from oral surgery. Del. Walter E. Fauntroy, one of Tucker's most ardent supporters in the primary, was out of town.

Tucker's solitude and the absence of Fauntroy and Washington were somewhat symbolic of the moving-close but-not quite there unity that continues to be a major target of the Barry campaign as the countdown period to the Nov. 7 general election enters its final two weeks.

Barry won the primary with about 35 percent of the vote and, in the view of most political observers, has merely to unite a sufficient number of the city's Democrats to become the next mayor.

Nearly 80 percent of the registered voters in the District are Democrats, and Barry has the bulk of the support of some of the major interest groups in town, including organized labor, churches and businessmen.TArthur A. Fletcher, the Republican nominee, who has raised far less money than Barry for his campaign, said yesterday that he thinks the contest will officially enter its pivotal period tonight at 7 o'clock. It is then that the first of four televised joint appearances by the two will be broadcast on WJLA-TV (Channel 7).

Fletcher's campaign has recently been bolstered by the addition of a new campaign manager, more - but still sparse - funds and increasing publicity, nevertheless, Fletcher, a relative unknown in local politics, will have to rely on his performance in the debates for the last-minute surge of support he feels he needs to win, he said.

Tonight's debate, Fletcher said yesterday, "will be quite decisive in terms of cementing those who allegedly want Marion as well as those who want me."

Fletcher is concentrating his political thrust in Ward 3, which includes nearly half the city's 21,500 registered Republican voters. "We think we can equal Marion in Ward 3," Fletcher said yesterday. "And the situation in all the other wards is as fluid as you have ever seen."

The Barry campaign expects to win in all eight of the city's wards, including Ward 3, which was Barry's strongest ward in the primary.

The slightly elusive search for party unity among the Democrats is viewed by city political observers as having more symbolic than practical effect in the campaign.

Although there is persistent talk in political circles that many disgruntled Tucker and Washington supporters are privately backing Fletcher, few have emerged yet. Several leading there would be mass defections to Fletcher.

Rather, they said, Barry would have to concentrate his efforts on getting a large enough percentage of the vote to establish broad-based popularity beyond his minority candidate status as the top vote-getter in a close, three-way winner-take-all primary.

Democratic Party leaders began convening meetings shortly after the primary in an effort to put together a united front. The first meeting became stalled by disagreements over a proposal to raise money to pay off the debts of the two losers in the mayor's race. Tucker and Washington.

According to reports filed with the D. C. Board of Elections and Ethics, Washington's campaign spent $265,532 and owes $68,414 to creditors but has only $2,465 on hand. The Tucker organization spent $361,353, but has outstanding bills of $51,012 and $2,722 on hand.

Representatives of the party's City Council nominees opposed raising money only for the mayoral candidates, so the plan was scrapped, sources said.

After an aborted attempted on Tuesday, an agreement was reached Wednesday by which the party would put out a sample ballot, have a huge city-wide rally Oct. 29, and raise funds for voter education efforts.

Each of the candidates will be responsible, however, for raising money to pay off his own debts, and that is expected to be difficult.

While the Barry organization is not taking the general election campaign lightly, it has already assembled a transition team to begin work on programs and to take a close look at the city bureaucracy that Barry will inherit if he wins on Nov. 7.