The billboards went up a few weeks ago. Dramatic and elegant, they portray a pensive Martin Luther King Jr. in shades of black and white. There is nothing more on them except a date: Jan. 20. A local advertising company raised 10 of the sidings around town to remind Atlantans that a new holiday approaches.

Not everyone needs reminders. The Atlanta Chamber of Commerce, City Hall and the Martin Luther King Center for Nonviolent Social Change have been scrambling for corporate contributions to a local holiday parade. King's home town, which expects to receive national attention during the holiday, hopes to mount a worthy extravaganza.

Yet among whites elsewhere in the South, a different attitude sometimes surfaces. Not long ago, the mayor of Claxton, Ga., was asked what his town would do for the holiday. Not much, he reckoned: "It's just not something we can do without irritating the taxpayers. If they want to have something in the black community, that's fine, but the city itself will not participate."

Why? Apparently the mayor believes that while blacks may owe King a debt of gratitude, southern whites owe his memory nothing.

Is he ever wrong. Two decades after the South got on with the business of enfranchisement and desegregation, this much is clear: The social justice that King and the civil rights movement forced upon the region was perhaps the best thing that ever happened to it.

If Martin Luther King was a latter-day Moses who led southern blacks toward full equality under the law, he did even more for southern whites. He led us toward the milk and honey of America's economic mainstream. The business boom that Atlanta and other parts of the South have long enjoyed would have been meager stuff indeed without King and the movement.

The reason is simple enough. Ultimately, social justice means efficiency and stability. If the movement did not create today's business boom, it did build an environment that could sustain high-quality investment and growth.

No longer was scarce money squandered on dual sets of schools, colleges, stores, restaurants and the rest. No longer was a major part of the southern work force denied real jobs and decent wages. No longer was the southern caste system allowed to undermine the work ethic among blacks and whites alike.

Suddenly the South was an attractive place in which to invest. In the five counties of metropolitan Atlanta between 1960 and 1972, service jobs increased from 50,350 to 105,900; manufacturing jobs from 85,050 to 112,800; retail jobs from 60,150 to 115,500, and wholesale jobs from 38,850 to 69,500.

Legal segregation had shackled everyone. When it was finally gone, areas that were ripe with economic potential took off. Even areas that saw little actual development reaped some benefits. The wealthier metropolitan Atlanta grew, for example, the more money state coffers held for health, education and welfare throughout Georgia.

Of course, there is a nagging irony here. While the economic benefits have touched rich and poor, the biggest beneficiary has been the middle class. In this category, far and away, whites have gained the most.

For blacks, while the civil rights movement delivered full citizenship, it didn't solve inequities that stem from poor education and historical discrimination. But for whites, it allowed mainstream southerners to become mainstream Americans. It opened the region to a business climate that was to pay handsomely for skills they already possessed.

Two decades after the end of the Civil War, Henry Grady, editor of The Atlanta Constitution, wrote that white southerners "are thankful that the issues at stake in the great Civil War were adjudged by a higher wisdom than their own." Grady and his fellow "New South" boosters new that economic development could come about only if the South became one with the nation.

Tragically, their aspirations foundered on the twin mistakes of disenfranchisement and segregation.

No, Martin Luther King did not end these two evils by himself. The federal courts and a cast of thousands inside and outside the movement played major roles. But as a symbol of the struggle to reinstate the South as a full-fledged part of the country, the martyred pastor of Atlanta's Ebenezer Baptist Church will do nicely.

On Monday, communities throughout the South may rejoice that the issues at stake two decades ago were "adjudged by a higher wisdom than their own." The King holiday is for everyone, but especially for southern whites. Even those who are blind to the human goodness of his work have tasted its fruits -- and liked them.