Facing a powerful Republican gubernatorial challenge in November, Democrats are waiting to see if their primary Tuesday produces a double political miracle.

Lt. Gov. Mike Daniel (D), front-runner in the four-man race for the nomination to succeed popular, two-term Gov. Richard W. Riley (D), has emptied his campaign treasury and gone into debt in a gamble to avoid a runoff. If he succeeds in winning more than half the vote, he would be the first Democrat since 1962 to win a contested gubernatorial nomination without a runoff.

But that would be nothing compared to the precedent-shattering possibility that State Human Rights Commissioner Jim Clyburn (D) might upset Secretary of State John T. Campbell (D) and become the first black Democratic nominee for statewide office in South Carolina history, a development party strategists think would boost turnout for the whole ticket in November.

The betting here this weekend is that Daniel will be forced into a runoff and Clyburn will fall short in his challenge to Campbell. But strategists in both parties agree that Democrats need a break to maintain the near-monopoly on the governorship they have enjoyed since Reconstruction.

In a bid for permanent realignment of South Carolina, Republicans are fielding the "dream team" of Rep. Carroll A. Campbell Jr. of Greenville for governor and Rep. Thomas F. Hartnett of Charleston for lieutenant governor. With roots in two of the three major metropolitan areas, ample financing and established political identities, they pose a real threat. Democrats have controlled the governorship for all but four years this century; the lieutenant governship, without a break.

What University of South Carolina political scientist Earl Black calls "the most genuinely competitive election we've ever had" has not yet stirred the voters' blood.

As Riley's partner in education reform and economic development efforts the past four years, Daniel, 46, has led from the start of the Democratic nomination fight, but has yet to demonstrate any emotional appeal. His strongest challenge was expected to come from former Hilton Head developer and Winthrop College president Phil Lader, 40, who attracted some key Riley allies and reform-minded Democrats.

But Lader was embarrassed early this spring when a state audit questioned the legality and propriety of expenditures he authorized at the college. Some polls have showed him barely ahead of retired judge Frank Eppes, 63, of Greenville, who has run a folksy, underfinanced friends-and-neighbors campaign against "the slick Madison Avenue candidates," Daniel and Lader. State Sen. Hugh Leatherman (D), 55, of Florence is generally thought to be trailing.

While the campaign has been polite by comparison to the donnybrooks South Carolina Democrats staged in the years when their nomination was tantamount to election, Lader has run TV spots accusing Daniel of turning his back on a dangerous toxic-waste dump in his home county and Eppes has charged the front-runner's biggest contributor has profited from a chain of small business "incubators" -- buildings designed to house new companies -- for which Daniel helped arrange state backing.

With the Republicans waiting, Daniel is eager to prevent two more weeks of pounding from Eppes or Lader, considered the likeliest to make the June 24 runoff. Daniel said Thursday it would be "very, very difficult" to avoid a runoff, but with late tracking polls reportedly showing him just a few points shy of 50 percent, he decided to use a $200,000 line of bank credit and step up his TV campaign hammering Lader, in hopes of a Tuesday knockout.

State Sen. John Courson (R), the Republican national committeeman, said in an interview that if Daniel's gamble pays off, "it will give him an inordinate amount of credibility and maybe make him the next governor."

But Courson, like many others, said "the wild card" in the Democratic primary is the Clyburn-John Campbell race for secretary of state. Eight years ago, Clyburn, the top black aide to former governor John C. West, led in the primary for secretary of state but lost to Campbell, a former mayor of Columbia, in the runoff.

Campbell, 73, was reportedly urged by several party leaders to step down this year, but when he declined, Clyburn decided to challenge him. The 45-year-old Charlestonian has attracted support from major white business leaders and endorsements from the Columbia and Greenville newspapers. But Campbell has built a network of courthouse backing as the incumbent.

Neither candidate has made any direct racial appeals, but with blacks expected to comprise 38 to 40 percent of the Democratic primary, the racial overtones of the contest are inescapable. Campbell said in an interview that "I have the feeling that if I'm defeated, we may have a Republican governor . . . . I have that much strength." But most white Democratic leaders make it evident they would prefer to have Clyburn on the ticket.

Leatherman is the only gubernatorial candidate to endorse Clyburn openly, but Clyburn said he has received quiet assistance from the other three camps as well. Robert Coble, manager of the Daniel campaign, said, "We're all helping Jim financially because we feel he would be an asset in the fall." The GOP's Courson said, "With Clyburn on the ballot in a contested race, it will maximize black turnout" for all Democrats in November, "but if he's beaten Tuesday, you will see some serious [black] disenchantment with the Democratic Party."

Several Democratic strategists expressed concern at a possible anti-Clyburn white backlash to the planned nine-city "get-out-the-vote drive" this weekend by 1984 Democratic presidential contender Jesse L. Jackson. Jackson said his Rainbow Coalition has not endorsed any candidates, but added that Clyburn's challenge "tests the readiness of the Democratic Party for integrated slate-making and reciprocal voting."

Clyburn said, "I had absolutely nothing to do with" Jackson's plans, adding, "He is not part of my campaign at all."