This small hamlet is thriving. Desso's, the general store, does a brisk business, real estate prices are rising and a dozen or so out-of-state residents have settled, intending to make Vermont their permanent home.

What's happening in Jericho Center is happening all over America.

Since 1970, rural areas - which had been experiencing out-migration for decades - have been the biggest population gainers along with small metropolitan area (under 250,000 population). Together they have accounted for more than half the U.S. population growth in the 1970s. Major metropolitan areas of more than three million have stagnated or even lost population. The adjacent table makes clear the magnitude of the change.

Almost no one predicted this stunning reversal, and its causes and implications remain murky. Fundamentally, people may be voting with their bodies against the problems - crime, congestion, pollution - that they associate with bigger cities.

For the movement to small communities is remarkably widespread. It has occurred in every region of the country, even those considered to be in decline. In New Jersey, for example, Cape May County - the southern tip of the state - experienced a 26 percent population increase between 1970 and 1976. At recent congressional hearings, Agriculture Department demographer Calvin Beale reported that the new migrants consist overwhelmingly of the young (nearly 70 percent are under 35), that they are disproportionately white (only 6 percent were black) and that many of them "accept an income cut."

But the story is clearly more complicated than an antiurban malaise. Big cities traditionally lured people with jobs. Rural areas now display a new competitiveness.

In selected spots - West Virginia and Wyoming, for example - growth reflects the revival of the coal industry. The new rural vitality also constitutes a belated reaction to changes that occurred in the 1950s and 1960s: the expansion of the interstate highway system, the growth of air travel, the increasing availability of low-cost voice and data communications, and the growth of federal transfer payments - Social Security and unemployment compensation - in providing income.

All these changes have increased invididual and business mobility. Social Security and Medicare (whose benefits have increased faster than inflation) pump money into places and create jobs. Unemployment compensation makes seasonal work - common in the tourism and construction industries - more feasible. Air travel and better highway have made remote areas more accessible and, along with a huge rise in discretionary incomes, have spurred tourism and the recreation business.

Industry moved in response to many of the same changes - plus, often, the lure of low-wage, non-union workers. During the 1960s, manufacturing firms expanded significantly in rural areas, representing one-third of all nonfarm job growth.

Demographer Beale believes that all these forces are coalescing to create rapid job growth and encourage a convergence of urban and rural lifestyles. In contrast with the 1960s, about 75 percent of the new jobs are in "trade and services" - retail stores, banking, insurance, schools and hospitals. Beale envisions a more diversified rural economy, characterized increasingly by national (rather than local) tastes.

Come to Vermont and you see many of these forces in action - and also the conflicts they generate.

Ralph Monticello, an economist for the state planning office, believes that the three northern New England states - Vermont, New Hampshire and Maine - contradict the conventional image of Frostbelt stagnation. The figures are ambiguous. Between 1970 and 1977, the population of the three states rose 11 percent, nearly twice as fast as the U.S. average (6.4 percent). The number of jobs also is expanding rapidly, but unemployment rates still remain higher than in the rest of New England.

C. Harry Behney, Vermont's secretary of development and community affairs, thinks the state has a new asset in its ability to keep the best of its young workers.

"In the Fifties, when I got out of college, most of my friends left Vermont to find their green pastures in Hartford, Boston or New Jersey," he said. "In the early Seventies, jobs [in Vermont] dropped off, but the values had changed. People said they wanted to stay, and so they took low-paying job." Behney thinks the state still has a good pool of skilled workers. A computer firm that recently advertised for workers received more than 8,000 applications for 300 openings.

But there are problems. As the flood of applications suggests, there may be considerable underemployment and job frustration. Likewise, the state has adopted a stringent development law that requires major projects to pass stiff tests on everything from water pollution to traffic congestion. Behney touts the laws as insurance that Vermont will preserve the clean and picturesque environment that is its major asset.

Not surprisingly, though, much of the real estate industry regards the law as a plague. Its requirements undoubtedly curb the freedom of farmers to sell their land for homes and, with housing in short supply, may have raised prices.

In short, the new migration is not painless. Big cities, already with heaps of problems, may lose more of their economic base. Rural areas suffer growing pains. But, beyond that, no one knows very much. The "experts" didn't predict the start of this trend, and they may not predict its stop, either.