Two years ago, whenever Prince George's salesman Michael DiMarzo felt thirsty after work, he would drive the half-hour from his Landover office to Georgetown, where he would face what he called the "uppity-up" attitudes of the happy-hour celebrants.

These days he drives just minutes up the road to nestle among the ficus trees and ferns at Jasper's. Located in the parking lot of a Greenbelt shopping center in the shadow of the county's tallest office tower, Jasper's has quickly become one of the county's most popular restaurants and a leading watering hole for the county's growing number of young professionals.

"You have to look at it academically," said County Council member Richard Castaldi, who on a recent night ate his dinner at Jasper's, attended a meeting and returned after replacing his suit jacket with a blazer and his tie with a gold chain. "There's probably only a few places to meet people. Church, business, play . . . . A lot of people . . . Maybe they don't go to church."

Said DiMarzo, "Everybody in here has a professional attitude. It's not like going downtown where you talk to somebody and everybody goes, who's THIS guy?"

With its profusion of plants, frothy drinks and funky, "urban contemporary" music, Jasper's aims squarely at a market of middle-class people, both black and white, on their way up, the so-called "singles" crowd that is so much a part of the demographic profile of Alexandria, Dupont Circle or Capitol Hill. In Prince George's, with its more traditional landscape of single-family homes, large households and blue-collar workers, the influx of young professionals is a newly noticed phenomenon, slowly forcing its way into the consciousness of the marketplace.

Jasper's, which opened in July 1981, is one of the first responses to that market, the county's "first grown-up, intentionally sophisticated place," according to Washington Post restaurant critic Phyllis Richman, a native of Prince George's.

"This is the first place in the manner of a downtown restaurant, a very urban, big-city menu," Richman said recently. With its plum walls and forest-green carpet, fireplace and multi-tiered room, "there was an investment in glamor."

The $1.5 million investment has paid off handsomely, according to its owners: The company grossed $3 million in the first year of business, more than twice the amount projected, and is serving about 1,000 meals a day.

"It satisfied a lot of different needs," said coowner Alonzo (Buckey) Motley III. Motley and the other owners are so sensitive to such needs that when they discovered that some patrons felt intimidated by cloth napkins, for example, they switched to paper. To accommodate customers who are hearing-impaired, they hired several employes who know sign language.

While most of the patrons and staff are white, black patrons say they feel comfortable at Jasper's. Some area nightclubs in the past have been accused by blacks of discouraging their patronage through their choice of music and arbitrary admission policies. Jasper's chief disc jockey, Brian Howard, said he has never seen such practices there.

Jasper's also takes care to offer the security that suburbanites long for, with a dress code (no sneakers, no tattered jeans) after 9 p.m. and what coowner Patrick Noonan calls "an implied behavior code" enforced by cheerful and well-dressd doormen. "They make it so you can eat dinner and not have to look at scrawny-looking people," said Jill Becker, 22, of Greenbelt.

The upscale sophistication of Jasper's contrasts sharply with Motley's origins. Motley, 40, is the oldest son of restaurateur Berk Motley, who found his way into Ripley's Believe It or Not Museum for playing three clarinets while standing on his head. The elder Motley is the owner and chief attraction of Berk Motley's Sirloin Room in Colmar Manor, the last survivor of the once notorious Bladensburg strip.

"In the '30s, '40s and '50s, they had about 20 nightclubs, strippers, the whole thing. This was the hottest spot around," said Berk Motley, who bought his rustic-looking restaurant in 1948 and still does a nightclub routine every Friday and Saturday night.

But his son's was to be a different world. At the age of 14, the same age Berk had run away from home to join a tent show, Buckey Motley was parking cars and washing dishes in his father's restaurant. And Buckey Motley, fond of blue suits and sensible neckties, would never be seen wearing the bra with twinkling lights that his father donned as part of an act last summer. "He's always been more serious than me," said Berk.

When the younger Motley decided to build Jasper's, Berk thought it would be nice to have it next-door to the Sirloin Room, which he now calls the "old place."

"But Buckey wouldn't hear of it," said his father, who helped finance Jasper's. "Said the location's no good."

For Jasper's, Buckey Motley wanted the new Greenway plaza, located in a part of Prince George's where much of the county's development is going up. The restaurant is a stone's throw from the $60 million Golden Triangle Office Park anchored by the Capital Cadillac dealership and from the Maryland Trade Center, the county's tallest office tower.

The three owners, Motley, his brother-in-law Noonan, and former Baltimore caterer Frederic Rosenthal, spent 3 1/2 years studying the area's demographic and economic development. They discovered, said Rosenthal, that "it's a fallacy that the singles' crowd is gravitating toward the city. With the advent of high-rise living, condominiums, garden apartments, you have some upwardly mobile people in their 20s and 30s, making $30,000 a year and looking to invest that money. When you have a crowd like that, you have a market."

Their research told them of a county in transition. According to park and planning demographer Phillip Taylor, who has analyzed the county's 1980 census data, household size in Prince George's dropped dramatically over the decade, from 3.34 persons in 1970 to 2.89 in 1980, while the county's population increased only a half a percent.

The number of single-person households -- those who generally have more money to spend than other households -- jumped almost 100 percent over the decade, faster than any kind of household. The number of homes for singles living together and single-parent families also has risen rapidly.

Moreover, according to Taylor, singles live better than ever. Their income has risen faster than marrieds and faster than the rate of inflation. In 1970, for example, the median income for singles was $3,809; in 1980 it was $10,206.

Moreover, in 1970, most single-family, female-headed households lived in inner Beltway areas, mostly in low-rent garden aparments. By 1980, these groups had moved farther out and were concentrated in more expensive townhouses, Taylor said. He suspects the increased buying power of the female-headed household is one reason for such changes, as well as the local economy's transition from blue-collar to sales, service and other white-collar work.

Median income in the county still lags behind the rest of the metropolitan area, and all patrons of Jasper's aren't lawyers in blue suits. "Really, our crowd is a cross-section of America," said Noonan. "The first day we opened, our biggest seller was turkey club sandwich ."

There was one problem that day. They only had one toaster. "There were 40 orders for toasted club, and I had one four-slice toaster," said Noonan.

Things have gone more smoothly since. So happy are the owners about their formula that they are looking for a place to open Jasper's Two. They think they have found the right formula for the suburbs.

The singles who jam the bar five deep on a weeknight apparently think so too. From the entrance set several steps higher than the bar so arrivals can be scanned quickly, to the backgammon tables, to the nooks with stuffed chairs and dim lights, it is a place to look for that special someone, they say.

"It's the easiest place to pick up people," said 21-year-old Bill Sylvester from New Carrollton with a Donny Osmond face and a self-proclaimed "smooth rap."

"See, what you've got to do is work in the three beers with your buddies, and then you're on your own."

Spotting a likely prospect -- in fact, a prospect with a friend -- Sylvester sauntered away from his buddies. "Uh, hey, uh, how are you ladies doing tonight?" he asked, giving his hair a quick groom.