Republican hopes of embarrassing Jimmy Carter in three Southern governor races this fall are slowly turning to dust.

Less than a week before election day, GOP nominees in Mississippi and Kentucky are trailing their Democratic opponents by wide margins in public opinion polls.

And the narrow victory Rep. David Treen, the GOP hope in Louisiana, scored on that state's open primary last Saturday has led even his supporters to concede he will face an uphill fight in the general election Dec. 8.

This is a dramatic reversal from a few months ago when Republican loyalists were quietly predicting that 1979 would be the year of the big score for Republicans in the South, the year old Dixie would send a message to Carter and the Democratic Party.

"I was hoping we'd pick up two of the three seats anyway," said one highly placed Republican operative, who now concedes the party may be shut out in the three states with governorship on the line this year.

Ironically, Carter, who carried all three states in 1976, has had almost nothing to do with his party's hopes in his home region. Democratic candidates in Mississippi and Louisiana have treated the president like he had the plague. And John Y. Brown Jr., the Democratic nominee in Kentucky, has handled his connections with Carter so gingerly.

In Mississippi, Democrat William Winter has not only stayed clear of Carter, he has openly criticized him. "The problem now is ineffective leadership," he said during a televised debate. "We've seen it from Jackson. lWe've had ineffective leadership from a so-called businessman in Washington D.C.

Republicans, meanwhile, have pulled out the stops. The Republican Governors Conference had donated 21,000 to Treen, $25,000 to former Kentucky governor Louie B. Nunn, and $25,000 to Gil Carmichael of Mississippi. The Republican National Committee has contributed another $50,000 to Carmichael and placed three-full-time staff members each in Mississippi and Kentucky. And GOP presidential hopefuls John Connally and Ronald Reagan, both favorites among Southern Conservatives, have made appearances in all three states.

Republicans, of course, were the early underdogs in all three races. But with well-known candidates in each state, GOP hopes of picking off all three governorships weren't so ridiculous as to be dismissed out of hand.

The surprise is that today they are all still underdogs, Carmichael and Nunn by wide margins.

Their situations have absolutely nothing to do with national politics. Mississippi is a good case in point.

In a sense, this election represents a coming of age in Mississippi politics, a dawn of the politics of respectability.

"This is the high-water mark in Mississippi politics," says Bill Minor, a veteran of 30 years observing Mississippi politics and editor of the Capitol Reporter here. "I've never seen two people of such quality in one race in this state. Nobody will be ashamed of whoever is elected.

"I've never been able to say that before," continues Minor. 'We've punished ourselves too long in Mississippi by electing buffoons, racists, negativists and people who have become governor by attrition."

Both Carmichael and Winter come from the progressive wings of their parties. Winter, a former lieutenant governor, state treasurer and legislator, has long been thought "too liberal" to be elected governor here because of his endorsement of John F. Kennedy in the 1960 presidential race and his calls for racial moderation during the decade that followed. He is making his third race for governor.

Carmichael, the closest thing the Republican Party here has to an old warhorse, is making his second try for governorship. A car dealer from Meridian, he made his name in Southern politics in 1972 by collecting a surprising 39 percent of the vote against then-Sen. James O. Eastland, a Senate Institution.

Like Winter, Carmichael, 52, has a well-established reputation as a racial moderate, has gotten in trouble with his own party (for advocating gun control and backing Gerald Ford over Ronald Reagan in 1976), and was beaten in his last try for the governorship by now-Gov. Cliff Finch, who put together a "redneck and blackneck" coalition.

One of Carmichael's greatest problems this year has been that he and Winter both appeal to the same progressive, urban constituencies.

"If you've got two nice guys in the same race in Mississippi, the nice Democrat will win every time," explains Carmichael.

So Carmichael quit being a nice guy and started distancing himself from Winter. He portrayed Winter as a representative of "the old politics," and as a "national Democrat, a Carter supporter, maybe even a Kennedy man." He made a series of television commercials accusing Winter of profiteering during his 25 years in public office. And he told blacks that Winter is a "parlor liberal" who employs no blacks in his large Jackson law firm.

Initially, Winter ignored the attacks, focusing his campaign on his experience in state government. Then, he started pointing out "flipflops" in Carmichael's record, noting, for example, that Carmichael advocated gun control four years ago but now opposes it.Then he made a TV commercial showing mud being slung at a map of Mississippi.

But this offers little real flavor of the race, or the transformation of Mississippi politics during the last decade. A joint appearence by the two candidates before a meeting of the state NAACP last weekend does this as well as anything.

The meeting was in a dingy gymnasium on the south side of Jackson, not far from Jackson State University. Much of the state's black leadership was there, wearing three-piece suits. Many, like Aaron Henry and Charles Evers, were veterans of some of the nation's most brutal civil rights battles during the 1960s, a time when the governor of the state, Ross Barnett, once said "The Negro is different because God made him different to punish him."

Mississippi politicians no longer attack blacks; they court them. And every white candidate for statewide office was at the meeting, each promising more brotherhood than the one before.

Carmichael's pitch was an economic one. As a businessmen, he said, he'd hired dozens of blacks in his car dealerships, and as a governor he would create a bigger economic pie for blacks to get a piece of "Social integration is fine, but economic integration is fundamental to what you're trying to do," he said.

Winter's pitch was to the past. "I spoke out for equal opportunity at a time when few public officials did so," he declared. "Very frankly, those were costly positions for me. I probably would have been elected governor a long time ago if I hadn't put my neck on the line."

State NAACP President Henry said he was sold on Winter. Until this year, he said, "I thought he was too decent a fellow to become governor of Mississippi."