Presidential commissions on vast topics too often tend to churn conventional wisdom into a bland paste that congeals on deservedly unread pages. And no commission ever had a less promising origin than the one that derived from the Camp David "dometic summit" of 1979, which ended with President Carter's lamenting and lamentable "malaise" speech. But the Commission for a National Agenda for the Eighties has imparted momentum to a bold idea.

Calling for "long-range reorientation of federal urban policy," the commission urges the government to "let the market function and then assist people to adjust." Instead of emphasizing policies to create jobs in declining cities of the Northeast and Midwest, policy should encourage surplus population to migrate to the booming cities of the South and West. The implication is that perhaps government should not -- even if it could, and in any case cannot -- thwart economic dynamics such as the one that is shifting wealth and opportunity, but not yet enough population, from the Frost Belt to the Sun Belt:

"When the federal government steps in to try to alter these dynamics, it generates a flood of demands that may sap the initiative of urban governments via the expectation of continuous support."

Since 1970, Chicago, Philadelphia, Detroit, Baltimore, Milwaukee, Cleveland, Boston, Pittsburgh and Washington have lost at least 10 percent of their population, while San Jose, Phoenix, El Paso, Houston and San Diego have grown at least 20 percent. The commission suggests assisted shrinkage for cities in decline. It says that "cities are not permanent," which isn't quite the point. Cities are permanent; their characters and functions are not. There will always be a London, but there have been many Londons.

New York, for example, became a city suited to a population of eight million because excellent rail service, cheap labor and cheap money made it a manufacturing center. Its advantages are gone; it still has functions, but not for eight million people.

Felix Rohatyn, a financier involved in keeping New York solvent, warns that the impact of the 1980 election will be "inevitable and harsh" on the "arc of economic crisis" from Baltimore to St. Louis. To partially offset tax cuts and defense increases, there probably will be cuts in programs (for jobs, transportation, housing) that will affect "old America" disproportionately. In the oil- and gas-producing regions, federal cutbacks will be more than compensated for by revenues from gas and oil price decontrol, so local taxes can continue to decline, and local services can continue to improve, thereby attracting industry from "old America."

Rohatyn says: "Between 1980 and 1990, decontrol of oil and gas prices will generate about $120 billion of added revenue to the energy-producing region of this country." Much of this will come from the consuming regions of the Northeast and Midwest. And he notes that, judging by living costs and household incomes, the standards of livng of residents of New York and Boston already are more than one-third below those of residents of Houston, Dallas and Atlanta.

One way to encourage people to move to the Sun Belt is to encourage the boom there, thereby widening the disparity with the Frost Belt. Of course, urging government to favor the Sun Belt would be a bit like bidding the sun to rise. It will, unbidden.

In democracy, numbers tell. As the Sun Belt's congressional strength grows, its dominance will be seen in the allocation of federal resources: the writing of grant formulas, the locating of military installations, and so on. The congressional coalition of "old America" can fight a rear-guard battle, but it will be only that.

Still, regional rivalry is as American as . . . well, nothing is more American.

Before slavery split the nation along North-South lines, the fight over tariffs split the manufacturing North from the importing South. At the turn of the century, agrarian populism of the prairie states was fueled by resentment of eastern financial centers. Today, disputes about management of energy and other resources, including land and water, are dividing the Mountains West from the rest of the nation. And the influx of Latin immigrants may soon set parts of the South and West dangerously at odds with the rest of the nation's regarding language and other cultural matters.

Reason suggests that regional rivalries are inevitable in a complex nation that spans a continent and contains regions with different climates, resources, economies and ethnic stocks. History, and the latest presidential commission, underscore the fact that regional rivalry is a constant of American experience.