The worlds of Andrew Young, once the student at Howard University, once the mediator in the civil rights struggle, once the congressman from the New South, once the U.N. ambassador and potentially the next mayor of Atlanta, converged at a fund-raiser for his campaign last night.

Though the party had many of the faces from the old battles -- so many that Young called it "a meeting" -- the sentiment was that the mayoral election on Oct. 6 could say much about future political trends. "A lot of elections send a message," said Pat Caddell, Jimmy Carter's pollster who's doing the same for Young and has predicted a victory. Referring to doomsayers on the future of the cities and of black leadership and coalition politics, Young said: "We are going to show them it ain't so."

Last night's reception, held at a private residence, was Young's fourth out-of-Atlanta fund-raiser in the last month. Though he has the lead in the polls, his closest opponent, state legislator Sidney Marcus, has the lead in pocketbooks. "When Young ran for Congress the first time in 1970, the money came from the outside. His support is not that much different," said Stoney Cooks, his longtime aide and campaign manager.

Former Carter administration ambassador to Barbados Sally Shelton, one of the 14 primary organizers, moved last weekend from Washington to Boston, where she is a fellow at Harvard University. Still, she found time to organize support for Young by "literally stopping on the road for pay phones and using a pay phone in my basement." Said Shelton, "I have great faith in him; besides, I know this is something he always wanted to do." Another organizer, Washington attorney Robert Washington, said he planned to take off from work on election day and "do whatever has to be done in Atlanta -- that's my expression of commitment."

Before the party started, another sponsor, Mary King, said $8,000 had been raised here. Of the coalition this fund-raiser prompted, King, whose work bridged the years from the 1960s civil-rights movement to the 1970s Carter administration, said: "It was very natural to do it. If one group hadn't, another would have."

The guests included Del. Walter Fauntroy (D-D.C.), Reps. Pat Schroeder (D-Colo.), William Lehman (D-Fla.) and William Gray (D-Pa.); former ambassador to Mali Anne Holloway; Richard Moe and James Johnson, former aides to Walter Mondale; consumer advocate Esther Peterson; and former Women's Bureau director Alexis Herman.

Introducing the speakers, Schroeder bemoaned the changes in Congress and the White House. "The current White House thinks Diana Ross is Betsy Ross' sister. What kind of reality is that bringing to America?" she said, to great laughter. Referring to her congressional colleagues, she said, "All those guys with the blow-dry hair. They are all so media-conscious. They react like trained seals to whomever is handing out cuff links." Standing beside her, Young counseled, "This too shall pass away."

As five poets read their own works, a small group listened, but most of the guests worked their way through the rice salad, nic,oise salad, salmon, fruit, and raw vegetable buffet, and talked to Young. Washington Mayor Marion Barry said he was going to withhold any specific advice until after the election: "Then I can offer him my lessons from the varsity."

Young never skimped on his optimism. His initial problem of "Is he going to like Atlanta after he's seen the U.N.?" was overcome with rigorous campaigning. "But it's really fun because in cities, that's where politics really counts," said the former ambassador, congressman and civil rights point man.