Gil Carmichael, who is the closest thing this state's young Republican Party has to an old warhorse, was winding his way through the crowd at the National Tobacco Spitting Contest the other day when an old timer grabbed his arm.

"Gil, I voted for you before, but I can't go for you this time," the man said. "I'm a Democrat, don't you know."

That's exactly the kind of thing Carmichael doesn't like to hear. He is ensnarled in something this state hasn't seen in more than a century - a Republican gubernatorial primary. And it comes at a time when almost everyone Carmichael meets has an uncle or cousin running for some local office in the Democratic primary.

So Carmichael tells Democrats to go ahead and vote for their relatives, but if they want Mississippi to "have a businessman governor," to let their wife or daughter vote for him.

His opponent, Leon Bramlett, is a born-again Republican, a former state Democratic chairman who joined the GOP in 1976. He was recruited for the race by a group of wealthy Ronald Reagon supporters who have never forgiven Carmichael for helping swing the state's 1978 GOP delegation to Gerald Ford.

Encouraged by the election of Sen. Thad Cochran (R-Miss.) last fall, both Bramlett and Carmichael believe they have a good chance of becoming Mississippi's first Republican governor since 1876 - if only they can survive the primary today.

"These Mississippi Democrats want to try a Republican governor for a change," says Carmichael, 53. "The old Democratic myth is going out of business in Mississippi."

This would complete a revolution of sorts.

For a century, "Republican" was a dirty word here, carrying with it dreaded memories of Reconstruction and Yankee carpetbaggers. The party didn't even bother to field a candidate for statewide office in between 1883 and 1963. And it wasn't until Cochran's win last fall that the party captured a statewide race.

The party, however, has never been in better shape here. A total of 188 Republican candidates, including a handful of blacks, are vying for offices traditionally held by Democrats.

If a Republican should win the governor's chair, the national implications are obvious. Al three of the governorships up for grabs this fall are in southern states - Kentucky, Louisiana and Mississippi. Republicans have strong contenders in each race.

"What happens in these states may say a great deal about the Carter presidency," says Cochran. "Just think, what if Republicans win three governorships in the South? That doesn't sound very good for a southern president, does it?"

Six Democrats, some of whom have been cirsscrossing the state for more than a year, are determined to see that doesn't happen. But their campaigns have attacted little interest. "It's the quietest race I've ever seen in Mississippi," says one of the Democratic candidates, William Winter, a former lieutenant governor.

The explanation that Winter and most of the other candidates give is that voters are turned off on politics because of their disappointment with the administration of Gov. Cliff Finch, who put together a "redneck and blackneck" coalition to win four years ago. State law prohibits Finch from seeking a second term.

Bill Minor, editor of the Capitol Reporter and one of the state's most respected political observers, offers another explanation. State politics, he wrote recently, has never recovered from the politics of racial hatred that dominated campaign rhetoric for generations.

"Somehow, it seems the candidates in Mississippi have been looking for an emotional substitute for the old "nigger" issue, and what they have come up with is just political pap, sweetened to taste good to voters," he wrote.

Race isn't an issue this fall. In fact the only campaign with segregationist overtones is that of Democratic dark horse candidate Richard Barrett, a native northerner who graduated from Rutgers University.

The other significant historical departure in the race is the candidacy of Lt. Gov. Evelyn Gandy, a 58-year-old woman who looks as fragile as a magnolia blossom. She jumped to a big lead in the race and remains its biggest question mark.

Since she went to work as a secretary to the late U.S. Senator Theodore Bilbo 34 years ago, "Miss Evelyn" has held five elected and three major appointed jobs in state government. But her popularily remains an enigma to most politicians.

For most of her career, she has avoided controversy and even public appearances, depending on a "silent vote." This year her campaign concentrates on her experience rather than on issues. Still, many ovservers think she will be one of the two candidates to survive today's election. The two will meet in a runoff Aug. 28.

Winter, John Arthur Eaves and Jim Herring, a former county prosecutor from Canton, are the other leading contenders in an extremely tight race.Barrett and the sixth Democratic candidate, state Rep. Charles Deaton, are given little chance.

Herring has the endorsement of former senator James O. Eastland and a,pears to be the best financed and best organized of the Democrats. On the stump and in his television ads, he has tried to link Gandy to a series of state government scandals.

It's hard to tell if this, sells in Mississippi. Traditionally, elections here boil down to emotional contests between an urbane sophisticate or landed aristocrat and a fiery upcountryman, with the latter collecting the bulk of the farm and blue-collar vote and the former collecting the most liberal, urban and country-gentry vote.

Winter, an urbane Jackson lawyer, appears to be the chief heir to one of the roles. Eaves, a fiery orator and "reformed" segregationist, is the heir to the other.

Eaves, 43, is the most colorful of the Democrats. When he ran for governor four years ago, he wore white suits, drove a white Cadillac and spoke like a young George C. Wallace. This year he's changed his image. His suits are charcoal grey. He has dropped his membership in the Citizens Council, and his speeches have more Billy Graham than George Wallace in them.

He ends most of them reciting "The Ragged Old Flag," a patriotic ballad popularized by Johnny Cash a few years ago. A band plays the "Battle Hymn of the Republic" in the background.

In his attempt to build a coalition of blue-collar whites and blacks, Eaves was given a big boost by the endorsement of Charles Evers, the state's best known civil rights leader. But several other major black groups have endorsed Herring, and Winter and Gandy are thought to have strong pockets of black support.

On the Republican side, Carmichael, a wealthy auto dealer from Meridian, was viewed as the early favorite. He is well known, well organized and articulate. In two previous statewide races, he did exceptionally well for a Republican, winning 39 percent of the vote against then-Sen-Eastland in 1972, and 48 percent against Finch in 1978.

But the contest has developed into a tough ideological fight between the moderate and conservative wings of the Republican Party with overtones for the 1980 presidential race. Carmichael is still confident he will win. "There's only one way for him [Bramlett] to win," he says. "That's to try to discredit me and spend every dollar he can get his hands on."

Bramlett, an All-American end at the U.S. Naval Academy at the time Jimmy Carter was just another midshipman, is doing just that.

He has mounted a huge television campaign and has circulated literature that accuses Carmichael of having "liberal tendencies," being a "1976 Ford supporter," advocating gun control (a position Carmichael took in 1975 but now denounces), supporting the Equal Rights Amendment and being a "three-time loser."

In the same literature, Bramlett, a millionaire Delta planter, describes himself as a "conservative alternative," a Reagon supporter, a gun control opponent and the only candidate who can win in November.

He is running as a fresh face in government, an antipolitician politician. "I think people are looking around for someone who can go into office without a lot of political baggage around his neck," he told a reception in Ocean Springs last week. "My approach would be like Reagan in California. I'd search out the most qualified people and bring them into government."

Bramlett, 56, is winning some converts. "I voted for Carmichael and I worked for him before," says Bob Bell, a realtor from Ocean Springs. "But we have a choice this time, and I think Bramlett is the class candidate. Gil has gotten that liberal cast to him. He'll say anything to get votes."

The turnout in the Republican primary is expected to be very low, perhaps under 40,000 voters. This makes the value of traditional campaign activities, like TV advertising and factory handshaking tours, suspect.

The problem for both candidates is to find how to reach the tiny band of party faithful. "I wouldn't bet a nickel on this race because you just can't tell what's going on," says GOP national committeeman Clarke Reed. CAPTION: Four of the candidates in today's Mississippi gubernatorial primaries. Picture 1, Republican Gil Carmichael, who is in a tight race with Leon Bramlett; Democrats; Picture 2, Jim Herring; Picture 3, William Winter; Picture 4, John Arthur Eaves, who are challenging Lt. Gov. Evelyn Gandy.