Bush and Buchanan Plunge Into South : Campaign: The President heads for Florida as his Republican rival fields tough questions in Louisiana.

President Bush and Patrick J. Buchanan embarked on grueling marches across the South on Wednesday, Bush in search of a convincing victory that would end the challenge to his leadership of the Republican Party, and Buchanan demanding that Bush himself drop out of the race.

While campaigning in Shreveport, La., Buchanan said Bush cannot win reelection in the fall. The President, he said, is in danger of becoming “a Republican Jimmy Carter”--a reference to the one-term Democratic President who lost to Ronald Reagan in 1980.

Bush, in turn, touted his victories in Georgia, Maryland and Colorado as emblematic of his popularity. “We won everything and we’re going to keep on winning everything,” he said as he set out for Florida on a six-day trip that will take him to as many as four states a day in preparation for the Super Tuesday contests in 11 states next week.

But the victories Bush has been achieving lack the knockout punch that the White House would like, forcing him to focus on his Republican rival rather than on an uncertain Democratic opponent.

Buchanan, buoyed by his 36% showing in Georgia and 30% tallies in Colorado and Maryland, was talking about a knockout punch of his own. He crisscrossed Louisiana and Oklahoma, where Bush will campaign later in the week.

The President, Buchanan said, should quit for the good of the party. “He’s losing all the Reagan Democrats, he’s losing the independents, he’s losing that segment which is a swing vote in the general election. And he’s losing to a candidate who 12 weeks ago was a television commentator”--a reference to Buchanan’s former role on CNN’s “Crossfire.”

Speaking to reporters in Shreveport, Buchanan conceded he did not expect Bush to throw in the towel. The challenger said he had left Bush’s legs “a little wobbly” but still needed “to find a place where we can put him down right on the canvas.”

White House Press Secretary Marlin Fitzwater laughed off the suggestion. “Buchanan has finally lost his senses,” Fitzwater said. “Buchanan has gone Looney Tunes on us.”

Regardless of such broadsides, and the concerted efforts by Bush and his aides to put the most upbeat stamp they can on the results of the primaries, polls of the voters suggest problems for Bush in the long run.

Among the findings:

* Bush has been unable to persuade voters that he is concerned about the problems of average Americans.

* The “gender gap” that troubled Bush in 1988 has at least temporarily disappeared. He is consistently attracting more support from women voters than is Buchanan. But this could mean that what overall strength he can demonstrate in the primaries could be diluted if these voters, no longer concerned about Buchanan, switch to the Democrat in the autumn.

In Florida, Bush continued to seek political mileage out of the Persian Gulf War, which Buchanan opposed before it began but supported once it did.

On Wednesday, the allied commander, retired Gen. Norman H. Schwarzkopf, appeared with the President at a fund-raising luncheon in Tampa, Fla. In a short, no-nonsense speech, he spoke of others who “were bending like reeds in the wind” before the war began--an obvious reference to Buchanan. But, Schwarzkopf said, “my commander in chief . . . had the courage to be unwavering.”

Buchanan went on the attack himself. He said Bush was winning primaries but “losing the debate.”

Taking cues from exit polls finding that about a quarter of his Georgia supporters would not vote for Bush, Buchanan supplemented his standard campaign appeal with the new claims designed to question the President’s electability.

“Mr. Bush’s base is rapidly being reduced to the hard-core Republican base that any nominee will carry in a general election,” he said in Shreveport. “I think if we get one or two victories over Mr. Bush, that big hollow army is going to cut and scatter and run.”

Campaign aides expected Louisiana to provide Buchanan’s best chance to beat Bush. In fact, the state GOP chairman, William Nungesser, has endorsed Buchanan and reiterated that endorsement as the candidate campaigned there.

On a 19-hour workday that was to end in Tulsa, Okla., Buchanan and his aides acknowledged that having to campaign in so many states in the next week would pose a challenge. After relying on intensive campaigning in New Hampshire and Georgia, Buchanan said grimly in Baton Rouge: “The number of primaries increases and the span of time diminishes.”

Buchanan also found himself facing some of his sharpest questioning yet from Louisiana reporters who asked at a series of campaign stops that he set himself apart from fellow Republican presidential candidate David Duke, the former Ku Klux Klan leader and neo-Nazi who is on the ballot here.

Both Buchanan and Duke oppose affirmative action, the 1991 Civil Rights Act and free trade. Buchanan touts his campaign as “America first”; Duke accuses Bush of putting “America last.”

Duke, a former Louisiana state representative who lost a run for the governorship last year, has urged his supporters to vote for Buchanan in any state in which he is not on the ballot--as was the case in Georgia, Colorado and Maryland Tuesday.

Throughout the campaign, Buchanan has taken care to note that he did not solicit Duke’s endorsement. He has tried to ignore him but has avoided direct criticism, referring to him as “that gentleman.”

Early in the day, he sought to maintain that hands-off stance, emphasizing only that he comes from a Republican background and that Duke was originally a Democrat. But ultimately Buchanan moved to put new distance between himself and his controversial rival.

“Things that have been said and done by Mr. Duke in the past are well worthy of condemnation,” he said at a news conference in Lafayette, La. “And that includes marching in that Nazi uniform and membership in the KKK.”

Gerstenzang reported from Florida and Jehl from Louisiana.