The Civil War is the explanation of, if not an excuse for, the South's feeling ill-used by Fate. But now the South is contemplating delicious revenge in the form of an early regional presidential primary.

With that, the South could throw its weight around in a way it has not been able to since the third day at Gettysburg. An "Awesome Tuesday" (it would make 1984's "Super Tuesday" seem tame) could threaten the Republican Party's hold on the presidency by loosening the grip of liberals on the Democratic Party's nominating process.

In the two months since Charles Robb, recently retired as Virginia's governor, organized a Democratic sweep in his state, Democrats have been busy examining the obvious with a sense of discovery. They are noticing that the South, which used to be spoken of condescendingly as "ready to join the mainstream," is a mainstream.

Virginia is symptomatic of Democratic problems. Since 1948, only one Democratic presidential candidate (Lyndon Johnson, in 1964) has carried Virginia. Before Robb's two terms, Virginia's governorship had 12 Republican years.

Today many Democrats, with their crippling habit of thinking too cautiously, are saying: we need a southerner -- Robb, or Gov. Mark White of Texas, or Sen. Sam Nunn of Georgia -- for vice president. But why just vice president? Nunn is conspicuously more able than anyone who is apt to be put ahead of him on the ticket, so it seems clear that Democrats have not kicked the habit of condescending to the South.

They should consider this. Since 1948 (when they won with a man, Harry Truman, from a state that had considerable Confederate sympathies -- the state in which Dred Scott went to court), they have won just three presidential elections, with three different candidates, and two were from states of the Confederacy. Here are some other facts calculated to freeze the marrow of Democrats:

William Schneider of the American Enterprise Institute notes the different composition of support for two Middle Western liberals who got 41 and 42 percent of the national vote -- Adlai Stevenson in 1956 and Walter Mondale 28 years later. Mondale did better than Stevenson among women, blacks, Jews, college graduates, professionals. Stevenson did better than Mondale among men, union members, blue-collar workers, Catholics and white southerners. The Democratic Party, says Schneider, has become less populist and more liberal as the country has tended toward what Reagan embodies: populist conservatism. Both populism and conservatism have strong southern pedigrees, and southern accents.

Since Roosevelt's death, no non- southern Democratic presidential candidate has won 50 percent of the national vote. While Mondale was carrying just seven southern congressional districts, more conservative Democrats were winning 73 southern seats. In 1936, 85 percent of white southerners voted for Roosevelt. Barely one-quarter of them voted for Mondale. More than half of Mondale's southern votes came from blacks. But since 1930, the black portion of the population has declined at least 20 percent in every southern state except Tennessee.

In this optimistic country, change implies hope. Liberalism lost its grip on the country when it built a government that showered benefits on client groups that then had a stake in the status quo. Such liberalism made the Democratic Party the party of government and government's clients (principally of public employees and the poor).

So in 1984, of the nation's 25 largest metropolitan areas, 20 voted for Reagan. Mondale's five were: home (Minneapolis-St. Paul), the one with the highest unemployment (Pittsburgh), the symbol of rust-belt distress (Cleveland), the host of the Democratic convention (San Francisco), and the home of bureaucracy (Washington).

However, Mondale did well with another set of 25 cities. He carried 20 of the 25 that lost population in the 1970s. Growth is fastest in the South and West. After the 1990 census, for the first time and for the foreseeable future, a majority of congressional seats and electoral votes will come from the South and West.

Suppose (this may be supposing too much) a regional southern primary produced a decisive result -- say, Nunn 50 percent, Hart 25 percent, Jackson 10 percent. Democrats might have a "southern strategy" thrust on them, and might wind up competitive, nationally.

How many states must cooperate to produce a critical mass for a regional primary? Perhaps seven. Richard Scammon, who knows more about elections than can be good for his peace of mind, offers this criterion: enough states to get the morning network news shows to cover the primary from, say, Atlanta.

We have arrived at the Maria Shriver Theory of History. Ye Gods.