More than 200,000 people within a seven-mile radius. Median family income of more than $17,000 a year. Good roads, good parking, low unemployment. But no shopping center less than 21 years old.

Last week, that began to change. The Shopco Company, a New York developer, broke ground for a shopping center in Laurel that will be the largest between Washington and Baltimore. The company thinks it has made a better bet than many of the patrons of the nearby racetrack.

What is coming is an enclosed mall, covering almost 71 acres, housing about 180 stores, costing about $25 million to build, providing almost one million square feet of sales space.

When it is finished in two years, Laurel Centre will be larger than Landover Mall, White Flint Mall, Columbia Mall or Prince George's Plaza - larger, in fact, than all but three shopping centers in the Washington area.

Laurel Centre will be grafted onto the existing Laurel Shopping Center, and will more than double the number of stores and the square footage of the old center. Like the existing center, the mall will sit just west of U.S. Rte. 1 and just south of the center of town.

While Bloomingdale's and the Sans Souci will be absent, Laurel Centre will have trendy stores and a range of restaurants the likes of which Laurel has not seen before.

The mall's decor will also be a considerable step up from the auto sales lots and fast-food restaurants that dot nearby U.S. 1.

Exposed wooden beams will be featured, and plants and shrubs will be numerous. At the center of the mall will be a brightly colored, pie-shaped group of boutiques on a carousel. The whole pie will revolve once an hour.

All this in Laurel? Little tobacco-farming, horse-breeding, poor-relation Laurel? Yes, says H. Joseph Edwards, president of the Greater Laurel Chamber of Commerce, who adds that it shouldn't come as that big a surprise.

"We have always expected Baltimore and Washington to grow towards each other, and the center will make it possible," Edwards said. He acknowledged that the new center cannot prosper on Laurel's population of 65,000 alone. but he said he expects the shopping center to touch off housing starts and population growth in the Laurel suburbs, and to draw from many miles around.

"It'll be a monster, but an attractive monster," Edwards said. "It'll get this community more together than ever before."

But because the new center will be occupied mostly by new businesses, it will put pressure on the 80 merchants in the existing Laurel Shopping Center, just as that center has put pressure on the small shopkeepers along Laurel's Main Street.

One merchant in the existing center, who asked that his name not be used, said he is almost certain the massive addition will put him out of business.

"Why choose a store like mine that's 21 years old when you can choose one selling the same thing that's brand new? he asked.

Meanwhile, merchants along Main Street, a picturesque, two-block-long stretch of small specialty shops about a mile north, are similary worried.

Just last year, the Main Street Merchants' Association staved off doom with a federal grant. The money went for upgranding of sidewalks, parking and lighting, all of which were far below the standard of Laurel Shopping Center. Now Main Streeters worry that an even larger shopping center will prove too formidable.

"We just can't compete," said one merchant, whose family has run shops along Main Street for two generations. "Maybe we can become a Georgetown sort of thing, but without that, we'll be in trouble."

Shopco has given every sign of being a good neighbor, however. "They didn't come in here like city slickers trying to tell us how to do everything," said one source in Laurel's government.

In addtion, the company has pledged to give its mall both a local flavor and a flock of tenants. The symbol for Laurel Centre will be in the shape of an oval, reminiscent of the nearby retrack, and more than a third of the tenants are expected to be small and local.

Since 1968, the developers of the existing center, Berman Enterprises, had contemplated the kind of expansion Shopco is about to undertake. "But to do this center alone would have meant growing as an organization," said Vincent Leahy, general manager of Berman Enterprises.

Wolford and Melvin Berman, the brothers who own Berman Entreprises decided not to do that, Leahy said. Berman Enterprises will manage Laurel Centre, but Shopco will finance, build, lease and maintain it.

Harold Yassky, a Shopco partner and its leasing specialist, said his company first started negotiations for the new center in 1976.

"We looked at this (Washington-Baltimore) corridor," Yassky said, in an interview in his New York office. "We saw there wasn't any exciting shopping facility and there was a huge population. We felt there must be tremendous slippage, people shopping elsewhere,"

According to Yassky, the new center expects to pull heavily from Fort Meade and Bowie, and to some extent from Silver Spring and Columbia. Still, the bulk of the potential customers will be local. While many of them now shop at the existing Laurel Shopping Center, Yassky said, some also turn up at Columbia Mall (12 miles away), Landover Mall (17 miles) and several centers along the Baltimore Beltway (20 miles).

Shopco's Laurel venture will be its sixth shopping complex in Maryland, and by far its largest. The company, the nation's ninth largest shopping center developer, owns and operates shopping malls in Frederick and Hagerstown, and shopping centers in Crofton. Baltimore and Hagerstown.

Leasing for Laurel Center began recently, and is running briskly, Yassky said. Among the major tenants will be J.C. Penney's, Lerner Shops (women's clothes) and Harmony Hut (records and tapes). The Hecht Company and Montgomery Ward are already at Laurel, and a fourth department store is being considered, Yassky said.

The Chamder of Commerce has strongly backed the new center, despite intial resistance from resisdents concerned about the traffic the center will almost certainly generate.

Edwards said much of the concern was laid to rest with the construction oof almost half s mile of new streets and turn-out lanes near the site of the center. Berman Enterprises and Shopco paid for them, not the city, Edwards said.

Traffic along U.S. 1 is expected to increase when the center opens, but not chokingly so. Edwards said. Meanwhile, construction is about to begin on a brigde over the nearby B&O railroad tracks.

The brigde, a state and federal project, will bring Rte. 197 traffic from the east almost directly to the center. At present, the road ends at the tracks. Without the bridge, cars tryinnnng to reach the new center would have to detour often-congested downtown Laurel.

All in all, the new center should answer once and for all the question Edwards says he has often heard: "Why can't Laurel have the same sort of first-class shopping as the rest of the area?"

"It was always just a question of timing," said Vincent Leahy. "We just haven't grown as the area has grown. Now we're growing. Itt's just a little late."