Can a year-round playground for the affluent make it?

Twenty years ago the mountain valley in which this tiny town is nestled was not much more than slumbery sheep and swaying groves of aspen.

But today this corrugated piece of Colorado is lined with rows of condominiums and crosshatched with ribbons of powdery snow that bear an ever-increasing number of brightly clad skiers. It is the site of some of America's latest and most expensive developments in the battle for the leisure buck.

For in this area sits Vail, a Cinderella-success story in the ski industry, still smugly sprawling down the valley. And nearby lies Beaver Creek, a recently opened Vail stepchild which its developers hope will become one of the world's most exclusive winter playgrounds.

From the start, Beaver Creek was planned as a year-round playground for the well-to-do. Golf and tennis are to be as important as skiing. Development is tightly controlled. Traffic is restricted (skiers must get to the slopes by bus).

By sometime in the 1990s, when the last nails are to be tacked in, the total cost of the resort area may be a half billion dollars or more. It will include a sports complex, shops, restaurants, a hotel, and a performing arts complex.

Beaver Creek's success, or lack of it, is being watched closely by other resort-builders in Colorado, as well as the ski industry in general.

Colorado faces stiff competition from neighboring Utah and other Western states. The state's estimated $2-billion-a-year resorts and tourism industry, of which skiing makes up about one quarter, has had a few hiccups lately.

Last season's dearth of snow cost the ski industry $95 million. Before that there were jitters about gasoline prices.

Not yet two years old, Beaver Creek is a virtual Gold Coast in the mountains. You won't find many mechanics staying here. Or ski racks clinging to 1957 jeeps. You will see furs and fistfuls of money. Gerald Ford is building a house here, as is a good chunk of corporate America.

The first ski lifts were officially sent humming up the hills last season after seven years of planning, nine years of haggling, and 52 environmental impact statements.

Beaver Creek was to be the site of the 1976 Olympics until Colorado voters balked at staging the games. In the meantime Vail Associates, developers of the site, spent $25 million sprucing up the place for vacationers.

There are to be homesites, condominiums, and townhouses in Beaver Creek, but none of them for the pauper. About 100 of the 250 available house lots have been sold so far (average price around $300,000, and the houses on them likely to top some cases, or some of the most expensive real estate in the world).

Some townhouses don't hurt as much: $255,000. Half-duplexes can be had for $ 600,000 to $800,000.

Roger Lessman, vice-president and general manager of Vail Associates' Beaver Creek division, says that after slow sales last year, ''We're at the point now where we could pick and choose the condominium deals we want.''

A lot of Mexican and Venezuelan oil money is flowing into the area. At last count 10 percent of the sales had been to investors from south of the border.

If the property sales continue, that will be good news for Beaver Creek, which, for lack of snow, jumped off to an inauspicious start at the ski slopes last year. This year the snow has been better, but the lift lines are still a bit thin.

''We're a new resort, not as widely known as we'd like to be,'' Mr. Lessman says. But he thinks recognition will come.

Still, winter resorts today are a lot more than lift tickets. Beaver Creek is going to have to lure year-round crowds.

''There aren't enough beautiful people to go around to keep the Aspens and Beaver Creeks going,'' says one Denver-based consultant. ''They (Beaver Creek) will also have to sell day-ski tickets and their summer programs.''

Charles Goeldner, director of business research at the University of Colorado in Boulder says, ''We are going to see real estate becoming a more important part of the resorts in the future, because to be a good resort you have to control what's around you,'' says Charles Goeldner, director of business research at the University of Colorado in Boulder and an industry consultant. ''You don't want a tin building in the middle of a ski resort that looks like an Alpine village.''