Jesse Jackson warns that what happens when he arrives in Atlanta is an open question, but Democratic leaders say they are confident intraparty tension will be resolved by the end of their national convention.

With word that former President Jimmy Carter has been asked to mediate the rift that opened this week between Jackson and apparent White House nominee Michael Dukakis, top party officials keep stressing harmony as they await the arrival of the disgruntled civil rights leader and the Massachusetts governor."I think we're going to have a unified, positive, constructive message coming from this convention," party Chairman Paul Kirk declared Thursday, promising Jackson would have a key role in the presidential campaign despite his loss to Dukakis and the choice of Texas Sen. Lloyd Bentsen as a running mate.

House Speaker Jim Wright of Texas, chairman of the convention, predicted in Washington that Democrats would come out of next week's conclave "arm in arm."

Jackson was somewhat conciliatory as he traveled from Chicago in a seven-bus caravan bound for Atlanta, saying he had accepted an apology from the Dukakis camp for not being told in advance that Bentsen had been chosen over him.

"We hope within a few days matters will be resolved," the Baptist preacher said in Indianapolis, his first overnight stop on the three-day bus trip. "We have every reason to seek a bridge and move beyond this impasse to victory this fall."

But Jackson charged he was still being excluded from the inner circle of top Democratic leaders making key decisions and said he was still weighing whether to wage a fight against Bentsen for the vice presidential nomination or fight for a laundry list of changes in the party platform.

Democratic leaders, with a history of nasty conventions, are desperately seeking a peaceful meeting where the only blood let belongs to Republicans.

Jackson disclosed Thursday that he telephoned Carter to facilitate such a meeting, saying he called the former president in Georgia "because I have so much respect for him."

"Maybe at some appropriate time he can play a real role . . . to get us on the right road," Jackson said, "the road to party expansion, the road to the kind of agreement that will allow all Democrats to leave Atlanta with their heads held high, a sense of esteem and great motivation."

Carter offered no immediate public comment, but Jackson said, "I did suggest such a meeting and he is willing if there is concurrence." The Dukakis camp had no immediate response.

A CBS News survey of Texas voters in the two days after Bentsen was chosen showed the Democratic ticket taking a lead of 48 percent to 44 percent over the Republican ticket led by adopted Texan Bush.

The telephone poll of 580 voters found Bentsen more popular than Bush by 55 percent to 44 percent - and Bush's negative ratings higher at this point than Dukakis's, 33 percent to 28 percent. The poll's error margin was 4 percentage points, according to the television network.

Bush, campaigning in Baltimore Thursday conscious of the Dukakis-Jackson split, told black Maryland business leaders that his administration would embrace minorities.

"We are the party of Lincoln. We've got to be open to the broadest base of Americans possible," he said to a crowd of about 600 at The Forum. "Sometimes we give up. We don't try hard enough. We don't open out arms wide enough."

Dukakis, meanwhile, took time out from his presidential campaign to tend to state business, signing a tough anti-drug bill and manuevering to settle a Massachusetts budget standoff.

Signing one bill on the hood of a state police car, the apparent nominee took a big step toward defusing Republican criticism that he is soft on crime by enacting some of the nation's most stringent mandatory sentences for drug traffickers, dealers and those selling narcotics to children.