CHARLESTON, S.C. -- The Democratic Party that rose from the ashes of the Civil War to rule this state unchallenged for nearly a century is in full-scale retreat before its increasingly bold and successful Republican opposition.

The Democratic gubernatorial nomination, once a virtual guarantee of election in November, has fallen by default to Theo Mitchell, a loquacious black state senator whose 1982 indictment on food stamp fraud charges ended in a hung jury and whose campaign manager and only paid staff member is a former VCR repairman.

Mitchell, an amiable Democratic backbencher known for supporting gay rights and prisoner rights in a state where those are hopeless causes, is, in the words of one longtime Democratic loyalist, "dead meat come November."

Even more worrisome to South Carolina Democrats is the party's overall decline. The Democrats also failed to produce a plausible nominee for the Senate, and Democratic dominance of the state legislature and state constitutional offices appears to be steadily eroding.

The Democratic Party is under assault throughout the Deep South, but nowhere is the party buckling more than in South Carolina. According to Democrats and Republicans, it is not uncommon for South Carolinians to say, when asked their party affiliation, "I'm white, aren't I?" by which they mean "I'm Republican."

In a state where the voting-age population is almost 75 percent white, such racial polarization between the parties is a recipe for Democratic defeat.

The white textile worker, farmhand and courthouse tobacco chewer have walked away from the party they once called home. In the Democratic presidential caucuses here in 1988, the state's white, rural voters simply didn't participate. Black civil rights leader Jesse L. Jackson crushed his white opposition, winning 54 percent to 18 percent for his closest competitor, Sen. Albert Gore Jr. (D-Tenn.).

In the Senate contest here this year, Strom Thurmond, the 1948 Dixiecrat candidate for president who converted to the GOP in 1964, is running virtually unopposed. Thurmond, who abandoned the battle against integration in 1970, now enjoys the formal endorsement of the current and former chairmen of the state Legislative Black Caucus, both Democrats.

The 87-year-old Thurmond's exalted status here is such that his easy path to a seventh term is no surprise. The far more dangerous development for the Democratic Party is that Carroll A. Campbell Jr., only the second Republican governor in South Carolina history -- the first was a fluke -- is effectively a lock to win a second term by a landslide.

Mitchell insists he can beat Campbell in November. "I certainly wouldn't be out here running for governor of South Carolina if I didn't think I had a chance to win," he said. But that optimistic assessment of his prospects is not widely shared.

Elected officials, party strategists and academics of both parties said they expect Mitchell to go down to defeat by about 65 to 35 percent. On the assumption that Mitchell will carry virtually all the black vote, which amounts to 25 to 28 percent of total turnout, such an outcome would suggest that Mitchell will get less than 15 percent of the white vote.

"It's going to be tough," said John W. Matthews, a black Democratic colleague of Mitchell's in the state Senate. "He might get five to 10 percent of the white vote; beyond that is very difficult."

In a state where the white liberal voting base is tiny, some of Mitchell's actions -- including his support for a demonstration backing the highly controversial rap group 2 Live Crew -- have sent chills down the spines of Democratic officeholders and created delighted anticipation of an ever-growing landslide among Republicans.

"Democratic officeholders are scared," said University of South Carolina political scientist Earl Black. Mitchell, he added, "has done almost everything he could to confirm white fears of liberals."

South Carolina, where the first shots of the Civil War were fired, has been on the leading edge of the ascendance of conservative Republicanism in the South.

In addition to Thurmond, who helped remove the carpetbagger image from the Republican Party and establish the GOP as the new political instrument of white hegemony, South Carolina has produced some of the most important figures in the two-decade-long rise of Republican conservatism. These include Harry Dent, who designed Richard M. Nixon's "southern strategy," and Republican National Committee Chairman Lee Atwater, one of the key architects of Ronald Reagan's 1984 landslide victory and George Bush's decisive win in 1988.

Participation in Republican primaries here remains relatively low, with only 107,000 ballots cast in the GOP contest this year. But that was a major surge from the 58,000 turnout of 1986. The Republican primary electorate in 1990 was more than 95 percent white.

Meanwhile, turnout in the 1990 Democratic gubernatorial primary nosedived. In 1986, 358,842 voters cast ballots in the Democratic primary, while only 213,387 went to the polls in June this year. Among whites, turnout fell from 1986 to 1990 by over 102,000; for blacks, turnout fell by 43,000.

In the Democratic primary, black voters are moving steadily toward majority status. In 1986, the turnout was 62 percent white and 38 percent black; this year it was 57 percent white and 43 percent black.

Donald Fowler, who served first as executive director and then as chairman of the South Carolina Democratic Party from 1967 to 1980 and is recognized as the party's eminence grise, anticipated much of the contemporary situation in a 1985 interview. "It's possible that sometime in the next five to 10 years the Democratic Party in the South would be a black party," he said.

Fowler argued that "for a long time now, Democrats generally in the South have been walking a fairly narrow line between using black support as an advantage, and letting blacks take over and the Democratic Party becoming a black party. Blacks, if they control the Democratic Party, will make it lose its viability. It will not be a viable party. . . . Blacks understandably are restless in the Democratic Party because they look at their level of loyalty and say 'Damn, if anybody deserves anything, we do.' And in normal political terms, that's true. But the other side of it is that if we gave them everything they wanted, it'd be a black party."

In the five years since Fowler made these comments, the Democratic Party in South Carolina appears to have crossed a tripping point for whites. Surveys by the Republican firm Ayres and Associates show that from September 1986 to August 1989 white voter allegiance in the state changed dramatically.

In 1986, the firm found that the GOP had a slight 30 to 24 percent advantage over the Democratic Party among white voters, with 46 percent describing themselves as independent. By August 1989, Democratic voter allegiance among whites had collapsed to 15 percent, while the white commitment to the GOP shot up to 54 percent. Among young white voters, the GOP held an extraordinary 61 to 7 percent margin over the Democrats. These findings were generally supported by University of South Carolina poll data.

The notion of a black Democratic Party, Mitchell argued, "is malarky. . . . I just think this is a panic that is being placed in there by some individuals in the Republican Party who are trying to polarize the races, to use scare tactics. These are some of the same ones who don't want me to run for governor; some are the ones who don't believe in a woman's rights; some are the same ones who don't believe in a worker's rights; some are the same people who don't believe labor unions have a role; some are the same ones who would condemn gay and lesbian people."

The problems facing not only Mitchell's campaign but the South Carolina Democratic Party are reflected in the political posture of John West, the Democrat elected governor in 1970 who is widely credited with moving the state to acceptance of the basic principles of racial equality and integration.

West, a lawyer in Hilton Head, is supporting the reelection of Thurmond. Asked if he will back Mitchell, the Democratic nominee for governor, West said: "I'd rather dodge that question."