Bert Lance gazed contentedly at the crush of 800 Georgia Democratic Party county chairmen and other leaders, mostly from the southern half of the state, and Sen. John Glenn of Ohio, who had come to court them at a gala dinner on the banks of the Ocmulgee River.

Glenn was just the latest in a blitz of Democratic presidential contenders who have traveled to the South since Lance took over as the Georgia party chairman last fall and began rallying his fellow state chairmen in the area to assert the South's new regional strength and be a moderating force on whoever becomes the party nominee.

Former vice president Walter F. Mondale has criss-crossed the region, as have Sen. Ernest F. Hollings of South Carolina and former governor Reubin Askew of Florida. Colorado's Gary Hart has dropped in. Since January, Glenn has visited nine southern states, several twice.

The dinner here, a tribute to Georgia House Speaker Tom Murphy, who has endorsed Askew, was Glenn's third trip to Georgia. He met with former President Carter, held forth at an "eggs-and-issues" breakfast near Atlanta, and conferred with Lance, who introduced him at dinner.

What is attracting the candidates is the gospel of New South politics as preached by Lance with the fervor of an evangelist at a tent revival.

His message is that no Democrat can beat President Reagan without winning the South: Florida, Alabama, Mississippi, Georgia, North and South Carolina, Virginia, Kentucky, Tennessee, Arkansas, Louisiana, West Virginia and Texas. No one can win the South, Lance contends, unless he is a "mainstream" candidate who can lure the middle-of-the-road voter.

It has been five years since Lance resigned as Carter's budget director with federal prosecutors hot on his trail over bank fraud charges of which he was acquitted. But Lance is back with a vengeance.

On just four days notice last month, he rounded up the Democratic Party chairmen of the southern states, all of them whites, and flew to Chicago to stump for Harold Washington in his mayoral race, making southern Democrats ostensible advocates of racial moderation for a party that will need the crucial black vote to beat Reagan.

"It was the right thing to do and it was good politics," Lance said.

He was host of the recent Jefferson-Jackson Day dinner in Atlanta that put all the presidential contenders except California Sen. Alan Cranston on stage together--and Lance back in the limelight. Gov. Joe Frank Harris has made Lance his political point man, with carte blanche to trade on national party ties Lance never lost.

Lance is using that commission to win new respect for the South--and for himself.

His name has been mentioned as a possible challenger to Republican Sen. Mack Mattingly in 1986, although a recent poll gave him about a 40 percent negative rating along with 90 percent name recognition.

Lance insists he wants nothing for his efforts. But one close friend said he would love to return to Washington as a top Cabinet official in a Democratic White House.

"Redemption is important to Bert, and redemption means a return to Washington, as a king or a kingmaker," the friend said.

But, in his comfortable Calhoun office, which he has dubbed Eagle's Nest, Lance waved at the pine trees dotting a lake outside his window and asked, "Why would I want to go back to Washington?"

He has recaptured control of the Calhoun National Bank, installed two sons as officers, built a large mansion he named Lancelot and emerged as a party power broker after a long ordeal.

Whatever his ambitions, Lance advises the Democratic presidential contenders to campaign heavily in the South, wear conservative stripes, pick a southerner as a running mate and avoid too avid courtship of traditional Democratic interest groups such as labor, blacks, feminists and homosexuals at the risk of alienating the mainstream.

To beat Reagan, he said, a Democrat will have to get most of the southern states' 153 electoral votes to offset traditional Republican strength in the West. Moreover, the southern states will have 26 percent of the delegates to the Democratic National Convention, half the number needed for nomination.

This, along with early primaries or caucuses in several southern states, makes the South pivotal, according to Hamilton Jordan, Carter's chief political strategist. Jordan has criss-crossed the South in his automobile with a slide show, spreading the gospel to governors and other party leaders.

The sermon begins with "Super Tuesday" down South--March 13, 1984--when Alabama, Florida and Georgia have primaries, followed four days later by caucuses in Arkansas, Kentucky, Mississippi, South Carolina and possibly Tennessee, plus Virginia two days after that.

Lance says he fears that favorite son candidates like Hollings and Askew might prevent any clear favorite from emerging in the primaries and foil his dream of the area being a broker in picking the nominee.

Glenn, however, appears to be the early favorite of many southern Democrats. In Macon, he struck a chord with conservative county chairmen such as Lewis Phillips, 62, a small trucker and a World War II bomber pilot.

"He talks my language," Phillips said. "He's the only middle-of-the-road candidate we've got. He's conservative, but he's also progressive."

Lance and other strategists say they believe Mondale will have to work hard to win the South, despite a superior organization. Phillips was even less optimistic.

"He's too liberal. He'd have to go before the press every day and denounce his liberalism. Otherwise, it's hopeless in the South."

Yet Mondale played well on a recent trip to Mississippi, where Gov. William F. Winter plans to endorse him, top aides said. Lance will not take sides.

"If someone like Gov. Winter comes out for Mondale, it will be an indication that here's a down-to-earth, common sense, moderate-conservative who's not out on any fringe," one aide said. "For someone who is not a mainstream candidate to fool Gov. Winter would be harder than slipping sunrise past a rooster."

Jim Quackenbush, Mondale's southern coordinator, said Mondale was planning more trips to the South. But Quackenbush, a former Carter volunteer, disputed Lance's role as a political guru.

"Everyone's been looking at the numbers," he said. "What they Lance and Jordan say is true, but they didn't come up with anything novel. I preach it every day."