ATLANTA (AP) _ Andrew Young's lackluster performance in last week's Georgia gubernatorial primary underscored the uphill battle black candidates are having as they seek some of the highest political posts in the South.

After slowly gaining a presence in local and state government, blacks are making unprecedented runs for office in a region once known for racial discrimination.

Though he failed to place first, Young has made it to an Aug. 7 runoff for the Democratic nomination for governor. Two other blacks are trying to win top elections elsewhere in the South.

In North Carolina, Harvey Gantt is the Democratic nominee trying to unseat Republican Sen. Jesse Helms; in South Carolina, state Sen. Theo Mitchell has won the Democratic gubernatorial nomination.

But Young, Gantt and Mitchell each are running against strong candidates, as well as a history that says voters in the predominantly white states generally cast ballots along racial lines.

Young, a former Atlanta mayor, congressman, U.N. ambassador and civil rights movement veteran, finished 12 percentage points on Tuesday behind the front-runner - Zell Miller, a four-term lieutenant governor.

Gantt, the former mayor of Charlotte, N.C., is up against Helms, a nationally known incumbent who has been in office 18 years. Mitchell, a state senator from Greenville, S.C., is challenging Republican Gov. Carroll Campbell, a popular incumbent with strong ties to the Bush administration.

Despite numerous differences between the three candidates, their opponents and their states, the three are bound by more than just the physical fact that they're black, said David Ruffin of the Joint Center for Political and Economic Studies, a black-oriented think tank in Washington.

''All these candidates are using politics to renegotiate the compact between society and blacks,'' said Ruffin, who edits the center's Focus magazine. ''All of them are looking for change. The big difference is in the conditions in which they're running.''

The nation has no black senators and one black governor, Virginia's L. Douglas Wilder, who was elected last year.

Since winning the Democratic runoff in North Carolina in June, Gantt has been on the road meeting voters, trying to offset the financial advantage held by Helms, an archconservative who some consider politically vulnerable this year.

''We think what we're doing is building support that is deep and won't be swayed by Helms' 30-second (television) barrages,'' said Susan Jetton, Gantt's press secretary.

Ms. Jetton said the Gantt campaign is finding plenty of anti-Helms sentiment across the state.

''He will have plenty of money and help in running against Helms,'' said Earl Black, a political science professor at the University of South Carolina. ''There is so much opposition to Helms that any Democratic candidate can expect good financing.''

But even some black supporters of Gantt aren't counting out Helms.

Tyrone Brooks, a black Georgia state legislator who supports Gantt, said he was nonetheless skeptical about Gantt's chances in the North Carolina election.

Brooks was asked about the North Carolinian earlier this month during a federal court hearing on a so-far-unsuccessful suit challenging the runoff provision of Georgia's election law. He testified that Gantt's runoff victory was an ''aberration'' and not representative of the climate for black candidates in Southern statewide elections.

''You can't say that because Mr. Gantt won in North Carolina, that we're going to win every runoff,'' Brooks said.

Many political observers said the second-place finish in the Georgia primary was a disappointment for Young, who was well known and ran as a moderate stressing his talent for attracting business investment.

But Young failed to win strong white support, and urban blacks failed to give him the overwhelming backing he counted on.

Young said the morning after the primary vote was counted that he was unsure why the black vote was smaller than he wanted.

Mitchell, on the other hand, attracted a sizable black vote in the Democratic primary and has been campaigning regularly at black churches, said Black.

Mitchell soundly defeated state Sen. Ernest Passailaigue, a white, in the Democratic primary, earning 60 percent of the vote. Election officials said voter turnout was low overall but that Mitchell was helped by the high black turnout. He remains the underdog in the general election campaign, however.

Keith R. Billingsley, an associate professor of political science at the University of Georgia, said Young's success with black voters may have been reduced because his two terms as mayor of predominantly black Atlanta were not an unqualified success among the city's residents.

''A number of black folks have told me they did not respect the way he ran the city, especially the police department,'' Billingsley said.

Race has not emerged as an overt issue in any of the campaigns, though there is a definite racial undercurrent, said Billingsley.

Young and Miller each have promised that the candidates' records will be the issue in their runoff campaign.

''They're going to talk about it (the record), and the voters are going to look at their color,'' Billingsley said.