Ronald Reagan swept to landslide victories in three states tonight, building a solid southern base as a foundation for the GOP front-runner status that is indisputably his.

Reagan was on his way to capturing most of the 114 delegates at stake in Florida, Georgia and Alabama as he buried George Bush, the only Republican who campaigned actively against him throughout the southern contests.

And Bush's prospects in the primaries of the North and Midwest appeared as politically perilous as those of his southern past. A new poll in next week's primary contest, in Illinois, shows that John B. Anderson, the Illinois congressman has moved ahead of Reagan and Bush.

And the specter of Gerald R. Ford's prospective candidacy looms threateningly over the Bush campaign as the former CIA director and former Republican campaign front-runner continued his politicking in the Midwest.

In Florida, with 90 percent of the precincts counted, Reagan had 57 percent, Bush 30 percent, Anderson 9 percent, Rep. Philip Crane of Illinois 2 percent and the rest shared by campaign dropouts.

In Georgia, with 98 percent of the precincts counted, Reagan had 73 percent, Bush 13 percent, Anderson 9 percent and Crane 3 percent.

In Alabama, with 90 percent counted, Reagan had 70 percent, Bush 26 percent and Crane 2 percent.

United Press International projected that Reagan would pick up 105 delegates, Bush nine.

Reagan, in a call to Florida supporters from Los Angeles, said, "Four years ago, a lot of people chuckled at Tommy [Thomas, his Florida chairman] because he said we'd carry Florida 2 to 1, and here we are doing it."

In Los Angeles, Reagan said he was surprised by the size of his victories in the three southern states. But in response to questions, he refused to say that the wins were a warning to Gerald Ford to stay out of the race.

"This is still early in the year," Reagan added. "We have a great many primaries to go."

Reagan's victories tonight were sweeping and broadbased. In Florida's populous Dade County, he led Bush by almost 3 to 1. A large part of this lead came from Cuban-American voters, who, while comprising just 5 percent of the total Republican vote in the state, cast their ballots for Reagan by about 4 to 1, according to an NBC network analysis.

In the St. Petersburg-Sarasota-Tampa region, where republican voters are mostly transplanted Midwesterners, Reagan held on to a commanding margin, even though a network analysis estimated that it would probably fall just short of a clear majority.

The fact that Bush and Anderson were able to stop Reagan from running away with the vote in this area of Midwestern Republicans is one of the few faintly encouraging signs for the middle-of-the-road and moderate wing of the party, as Republicans of that persuasion seek to find some way of stopping the growing strength of Reagan.

Bush received about one-third of the vote in this region, and Anderson received about one fifth.

The focus of the Grand Old Party's fight for the presidency now shifts to Illinois, where voters will make their views known next Tuesday.

And while Bush may be glad to get out of the South, the news from the North is not altogether heartening for his candidacy.

A Chicago Tribune poll showed Anderson leading in his home state with 33 percent, while Reagan was just a shade behind at 31, with Bush lagging at 20.

More than half of Florida's Republicans consider themselves conservatives, according to the NBC network survey, and among these, Reagan received 68 percent of the vote. Another quarter of the Republican voters said they were moderate, and here Bush was hurt by the mere existence of Anderson, who did not campaign in the state. Of that moderate Republican vote, Reagan received 46 percent, Bush 35 and Anderson 16.

The southern primary results are bound to be a factor in the political future of one prominent Republican who is not on the ballot in any of three states -- Gerald R. Ford. The former president planned to meet with some of the men who were his closest advisers back in his White House days to discuss whether it is too late for him to win the nomination.

One factor in their deliberations must be whether a belated Ford entry would only serve to divide the moderates and middle-of-the-road Republican vote between Ford and Bush, thus aiding the prospects of the one candidate Ford most wants to defeat, the man who almost wrested the nomination from him in 1976, Reagan.

In 1976, Reagan lost to Ford in Florida by 53 to 47 percent. But Reagan carried both Georgia and Alabama.

This year, Reagan entered the three primaries in the enviable position of a candidate who was already a front-runner, and was not looking to build a southern base to shore up his position.

On Saturday, Reagan swept to a landslide victory over Connally and Bush in South Carolina. The victory knocked Connally into the ranks of the dropouts, as he quickly joined Sen. Howard H. Baker Jr. on the campaign sidelines.

Bush, meanwhile, sought to dispel the memory of South Carolina by trying to close in on Reagan's lead in Florida. He shifted his travel schedule in the last days of the Florida campaign, adding stops within the state and dropping appearances in Alabama and New Jersey. Bush did this, his aides said at the time, "because his telephone bank cavassing had shown him to be gaining ground on Reagan.

But there is evidence that the Bush strategists felt they still had a way to go in Florida in those closing days. For money is the root of all politics, and the Bush advisers apparently did not feel confident enough of the gains they claimed to be making to make one final round of media advertising purchases that had been under consideration.

Bush's advisers had been weighing the purchase of new radio ads in populous Dade County, but only if they felt they had a chance of carrying Florida and needed to reduce the margin of their expected defeat in Dade County. The media time was never purchased.

The southern primary campaign produced few issues that sharply divided the ranks of the Grand Old Party. But in Florida, as in New Hampshire, Bush was hamstrung by one semi-issue: his onetime membership in the Trilateral Commission, a controversy that flew with him wherever he went, soaring on the right wing of the Republican Party.

The Florida Conservative Union took out ads in major Florida papers to attack Bush for having belonged to this organization, which was painted as the arm of a Rockefeller international banking conspiracy.

And at most stops, Bush had to explain to questioners that the Trilateral Commission is, in his view, just an organization to promote international cooperation between the United States, Western Europe and Japan, and Bush would add at every stop that some of Reagan's closest associates are also members of the group.

Bush said he would have liked to have done better in the South, but that he found some solace in the fact that "I went into Reagan territory and came out with nine delegates, maybe more."

"We were not as pleased with our results as we might have been," said Bush campaign manager James Baker. He said the Florida results had lowered Bush's expectations for Illinois, where he said Bush now hopes for "a respectable third-place showing." mjm