ATLANTA -- When Lee Atwater went into politics 18 years ago, he was part of a conservative, middle-class insurgency in the rural-dominated South, a suburban Republican uprising at a time when the dominant Democratic Party was shifting gears on civil rights.

Atwater, the former social chairman of Alpha Tau Omega fraternity at Newberry College, chose the GOP because he "was always an antiestablishment-type guy" and the Democrats were a "cigar-smoking . . . elite group that went around wearing three-piece suits."

Today, Atwater is no longer battling the "establishment." He is at the helm of Vice President Bush's presidential campaign, a drive that has the backing of much of the South's corporate elite and a near lock on the most prestigious members of a new Republican southern political establishment.

Here in Georgia, those backers include such movers and shakers in the business and financial community as Bennett Brown, president of Citizens and Southern Banks; Joe Rogers Jr., president of Waffle House; Fred Cooper, vice chairman of Flowers Industries; and Thomas Williams, retired president of First National Bank of Atlanta.

In 1976, the southern Republican Party led the unsuccessful intraparty insurgency against Gerald R. Ford, the GOP's incumbent president, as North Carolina, Georgia, Alabama, Arkansas and Texas cast their votes for the seemingly fringe conservative candidacy of Ronald Reagan.

Now, however, many of the leaders of the 1976 insurgency that defied the unwritten Republican rule that "you don't kill the king" are firm supporters of the heir-apparent to the throne -- lining up behind Bush, who is in some respects the most moderate of the Republicans seeking the nomination and clearly the candidate with the strongest links to the GOP establishment and strong links to the once-despised Wall Street wing of the party.

"Hell," said Clarke Reed, former chairman of the Mississippi Republican Party and a Bush supporter, "we've changed. We are the establishment." Said Lou Kitchin, a Bush consultant: "I'm a little bit older than I was in 1976," when he coordinated Reagan's campaign in the South. "Back then, it was a crusade. Now it's different, it's very different."

The Reagan years have radically altered the southern Republican Party in a process that is being accelerated by the Bush campaign and, to a lesser extent, by the campaign of Sen. Robert J. Dole (R-Kan.).

Among the cream of the southern political leadership, the overwhelming majority of endorsements have gone to Bush: the three governors who have made commitments are with the vice president, half of the region's national committeemen and women who are publicly and privately committed are with Bush and 22 of the 27 southern members of Congress who have endorsed are in the Bush camp, including 12 of the 17 GOP House members from the key states of Texas and Florida.

These endorsements of Bush reflect the conversion of the leadership of the southern Republican Party -- from an uprising rooted in 1964 candidacy of Barry Goldwater and the collapse of the old Democratic Party role as the protector of white supremacy -- to the status of a mainstream force in national and regional politics, now in control of five of of 11 governorships in the Confederate South.

The readiness of southern Republican leaders to back Bush also grows out of a geometrically expanding Republican voting constituency that has extended far beyond the hard core of conservatives who built the party in the black South. This constituency now includes the influx of voters from the North who have followed the movement of domestic and multinational corporations into the region.

"The conservatives are more mainstream," said Warren Tompkins, administrative assistant to South Carolina Republican Gov. Carroll A. Campbell Jr., who, with Campbell, was once part of the network of South Carolina conservative activists.

"One of our best lists is the list of new homeowners," James Morgan, Bush's southern deputy said in an interview at the campaign's Georgia headquarters. These newcomers, he said, are "middle management, well-paid, who want to live in the suburbs -- typical Republicans."

"When we call these people, the response is as good as from Reagan-Bush favorables" -- voters who were identified in 1984 as backing Reagan's reelection, Morgan said. These new voters are not the intense, antitax conservatives who provided Reagan's southern margin over Ford in 1976, but voters who are willing to support bond issues and higher sales taxes to finance expanded government services, new schools and better roads.

These heavily Republican new voters have turned suburban Gwinnett County into the fastest growing county in the nation -- the number of households there has gone from 55,311 in 1980 to 85,954 in 1985 -- and in the growing suburban neighborhoods of the South, they have changed the fabric and ideological tenor of the GOP.

Just 12 years ago, the Ford-Reagan contest revealed a deep ideological division in the southern Republican Party. Ford was successful in sections of Kentucky and East Tennessee where a moderate wing of the GOP had roots dating back to the Civil War and the tradition of Abraham Lincoln, and in Florida, where northern immigrants provided a substantial block of GOP primary votes.

Reagan, in contrast, routed Ford two-to-one throughout the Deep South where, until the early 1960s and the start of the civil rights movement, there had effectively been no Republican Party.

The extent of Bush support among early (1968, 1976 and 1980) Reagan backers is a clear demonstration of the moderation -- or dulling -- of the sharper edges of southern conservatism over the eight years of the Reagan presidency.

Such men as Florida National Committeeman Tommy Thomas and Texas National Committeeman Ernest Angelo would never have been seen as aligned with Bush in 1980, but now are loyal members of the Bush bandwagon. In South Carolina, where party leaders in 1976 put together a delegation that cast 27 convention votes for Reagan and only 9 for Ford, all the major Reagan supporters from 1976 and 1980 except one are with Bush.

The moderate-conservative split is not the central fault line in the 1988 battle for the presidential nomination in the South. Instead, the top contenders, Bush and Dole, are competing for support among party and local officials in a contest with little ideological content.

The lack of a moderate-conservative split is reflected in the failure in almost every section of the South of Rep. Jack Kemp (R-N.Y.) to gain a strong organizational base. The basic premise of the Kemp campaign is that he is the ideological heir to the leadership of the conservative movement that put Reagan in office.