COULD a Southerner finally win back the White House for Democrats in 1992 and end the party's dismal losing streak?Two Southern governors - Bill Clinton of Arkansas and L. Douglas Wilder of Virginia - now are among the leading candidates for their party's presidential nomination. Governor Clinton, who entered the contest yesterday, has spearheaded efforts to move Democrats away from liberalism and back to the middle of the road. Governor Wilder is a fiscal conservative known for his budget-cutting. Political analysts say these two men, both moderates, could play an instrumental role next year by helping Democrats win back some of the middle-class Americans who have given up on the party since the 1960s. However, analysts emphasize that even the most attractive Southern Democrat may be unable to reclaim the allegiance of these voters, who number in the millions, and break the Republican lock on Dixie. Claibourne Darden Jr., an Atlanta pollster, calls these former Democratic voters "Bubba." Bubba is "right at the middle of the middle class," Mr. Darden explains. "He's a high-school graduate, blue collar or lower white collar. He rides around in a pickup truck in the South with a gun in the back window. He's in construction, farming, factory, forestry, or he's an electrician, plumber, mechanic." Right now, Bubba loves George Bush. Clinton thinks he knows how Democrats can win Bubba back: first, by emphasizing work over give-away programs; second, by making sure that government programs help the middle class as much as the poor - through better schools, for example; third, by putting greater emphasis on values, particularly the value of personal responsibility. Experts hail the efforts that Clinton and Wilder are making to rebuild their party in the South and across the nation. Wilder, the nation's first elected black governor, won the endorsements of rural law-enforcement officers in Virginia, for example, which helped him convince voters that he wasn't just another soft-hearted liberal. Nevertheless, experts say that Democrats have dug a hole for themselves that is so deep that even the best efforts of Clinton, Wilder, or any other Democrat won't be enough to help the party climb out of it in this decade. Political scientist Earl Black at the University of South Carolina says Democratic strength has weakened so severely in the 11 states of the former Confederacy that the South now comprises the strongest Republican region in the United States. Dr. Black observes that by putting Southerners at the top of the ticket (Lyndon Johnson in 1964 and Jimmy Carter in 1976) Democrats managed to carry the region, and the nation, twice during the past 27 years. During that same period, every Northern Democrat who headed the ticket was trounced. But now Black thinks it may be too late even for a Southerner to ride to the rescue of the party. "It is going to be much more difficult for a Southerner to have the same degree of success as Carter had, for there are far fewer white Democrats in 1991 than in 1976," Black says. Darden agrees. He says even Carter's election was a fluke, a victory based on national revulsion over the Republican Watergate scandal, not on Carter's wide appeal to the public. To illustrate how severe the Democratic problem in the South is, Darden observes that with the exception of Carter's election, Democrats have carried only two Southern states since 1964 - Texas in 1968, and Georgia in 1980. Otherwise, it's been a wipeout. Tom Cronin, a political scientist at Colorado College and author of a best-selling textbook on politics, concludes: "I don't see any major hope for the Democrats right now. They are a party that has lost its sense of purpose." Even if Clinton got the nomination, Dr. Cronin says, "he has very little name recognition.... He has no foreign policy experience, except being a Rhodes Scholar. He does have experience in one important area, education. But [Education Secretary] Lamar Alexander and President Bush have stolen that issue." Robert Holsworth, a political scientist who closely follows Wilder's career, says the Democrats have two options for 1992, and neither is very attractive. "One is to come back and fight for the South with a Southerner at the top of the ticket, either Clinton, Wilder, or [Sen. Lloyd] Bentsen [of Texas, who ran for vice president in 1988]. "The second strategy for Democrats is to run a Northeast-Midwest-Western strategy." They would try to hold their traditional bases in the Northeast and industrial portions of the Midwest, while looking West for the additional electoral votes they need for a majority. The second strategy would acknowledge that the Democrats are fading badly in the South, and would play upon the party's strengths in the environment, education, and other domestic issues that resonate well in the West. Dr. Holsworth, who teaches at Virginia Commonwealth University, notes that in 1988, even though Dukakis lost in most Western states, he came surprisingly close in some of them. The bottom line: 1992 may serve only as a warm-up for candidates like Clinton and Wilder for 1996, when Mr. Bush will have to step down, opening the way for a stronger challenge by the Democratic Party.