The mood on the dance floor at the Sheraton Park Hotel was festive and upbeat at last week's Democratic Party disco with Rosalynn Carter -- even though the first lady left before the dancing started. But while President Carter and his local supporters feel they have the District's three electoral votes locked up, there is little enthusiasm among local Democrats about next Tuesday's election and a lot of worrying.

They are worried, not about Carter losing in the District, but about Republican challenger Ronald Reagan winning in the nation. They are worried about what that could mean for home rule, the federal payment and other matters dear to D.C. residents' hearts.

Meanwhile, at Reagan's District campaign headquarters, on the first floor of a posh 15th Street office building downtown, volunteers seemed oblivious last week to their candidate's expected defeat in the city. Workers are busy hand-addressing envelopes for a mass mailing, because, in the words of co-chairwoman Patricia Burns, "We can't afford anything else."

And at independent candidate John B. Anderson's Dupont Circle headquarters volunteer Marguerite Brunner was musing aloud that her efforts were all for naught, since Carter had the District vote wrapped up. "It's too bad the D.C. vote doesn't count," she said. "I can take them [Anderson voters] to the polls, but what good does it do?" "

The moods of the three campaigns closely reflects the development of the three presidential candidates' fortunes in the city -- the resignation of the Anderson supporters, the stubborn optimisim of the Republicans and the Democratics' unenthusiastic confidence. The later has caused Carter supporters to use anti-Reagan scare rhetoric to turn out a big vote here for the president.

Mayor Marion Barry has been spreading the word that Reagan's election will divide blacks from whites. D.C. Carter/Mondale campaign coordinator Barbara Lett Simmons, who is also vice president of the city's school board, says apocalyptically that Reagan's election would mean "the elimination of civilization as we know it." And D.C. Del. Walter E. Fauntroy, facing only minor opposition in his own reelection bid, says Reagan and the "far right, born-again Christians" will slash the federal payment to the city and threaten home rule.

Barry predicts that Carter will win with at least 60 percent of the city's heavily Democratic vote. Even so, he said recently, "Reagan's going to get a good vote here," and "Anderson's going to get a good vote."

That margin, while not nearly the 82 percent Carter won here in 1976 against former President Gerald R. Ford, would still ordinarily be enough to lull any campaign organization into relaxed self-confidence.

But the worry now plaguing the city's Democratic leadership is what happens to the District if their candidate loses the national election to Reagan.

The District is still inextricably tied to the federal government -- especially financially -- and there is a genuine fear among Democratic officials that a Reagan administration would be less sympathetic to District problems and less likely to be forthcoming with any increased self-government for the city.

"I think it (reagan's election ) would be not only divisive but a disaster here in Washington," Barry said Saturday. "President Carter has been good to us in terms of full budget autonomy and the transfer of prosecutorial authority."

Other Democrats agree, citing Reagan's unsympathetic public comments about home rule for the District, the absence of a home rule plank in the Republican Party platform and Reagan's particular less-government-intervention philosophy of fiscal restraint at a time when city officials are looking to Congress for help to solve a worsening budget crisis here.

At the same time, Democratic Party leaders acknowledge that enthusiasm for Carter has been lacking here as it has among Democrats nationally.

For example, the Gertrude Stein Democratic Club, the city's politically effective homosexual lobbying organization, chose to withhold its endorsement of any presidential candidate this year, rather than endorse Carter. Stein Club members, many of them supporters of Sen. Edward M. Kennedy (D-Mass.) who won the Democratic primary here earlier this year, ignored a personal plea from the mayor to endorse Carter and from some old-line Stein Club members who warned that a Reagan presidency would be a setback for homosexual rights.

"There are some sour grapes," said Carter coordinator Simmons. "If you're all about a charismatic personality instead of sound policies, then that makes it more difficult for you to make the transition. There is no question that the District has been in love with the Kennedys. People yearn for Camelot -- it's very intriguing."

Reagan supporters are stressing economic themes and taking their campaign directly to the city's black communities. Anderson's campaign, stalled here as it is nationwide, has its best hopes of taking votes from Carter in Ward 3, the predominantly white area of the city west of Rock Creek Park, especially among disgruntled Kennedy liberals. Anderson's District coordinator, Phil Johnson, a real estate broker and former Kennedy supporter himself, concedes that he has found little support for Anderson among blacks.

The only place where Anderson has found some substantial support here is among city homosexuals. The politically formidable homosexual community has split between Carter and Anderson, and a group called "Washington Area Gays for Anderson" has been running advertisements in the Washington Blade, a newspaper for homosexuals, telling its readers that Anderson is "the only candidate who fully and openly supports you."

Meanwhile, the Reagan forces -- who hope to capture 25 percent of the District vote Nov. 4 -- are mailing out one newsletter to 25,000 Republicans, Democrats and independents in key voting precincts at a cost of about $4,000 -- almost half the local GOP's total campaign coffer. The rest of the money will go for radio advertisements that will boost the Reagan-Bush ticket four times each day this week on three stations -- WOL, WOOK and WUST -- all with primarily black listening audiences.