It's a stripped-down supermarket where customers shop in a warehouse-like environment, choose from 3,000 grocery items instead of the usually 10,000 and bag their own groceries.

The store doesn't accept checks, doesn't sell small packages of meat or cheese and doesn't provide sacks for its customers.

But The Grand Union Co., which will open its new "Basics" store Sunday in Marlow Heights, said it does sell groceries, produce and meats at prices that are lower than competing supermarket chains.

The store is Grand Union's entry into the so-called box store market here.

The A&P company already operates five "Plus Discount" box stores here, stores that display merchandise in the original cardboard box sent from packing houses.

Supermarket chain officials say that the stripped-down stores enable them to charge lower prices because of reduced overhead and increased customer volume.

"A customer can expect to receive as much as 30 percent more merchandise for the food dollar," said Kenneth A. Brown, Grand Union's regional vice president.

Brown's declaration drew a skeptical response from officials of other Washington area supermarket companies.

"Thirty percent? I seriously doubt that," said Ernest Moore, a Safeway official.

"The individual's shopping basket determines what is the best [and spokesman for Giant Food, lowest price], said Barry Scher, a Stanley Coin, a division president of the chain that owns the Memcoo stores, said shoppers buying their "complete shopping needs" at Memco will save money there.

None of the three chains ruled out the possiblity of a price war. They said they will watch prices at the Basics store and will "be happy to accept any challenge."

During a tour yesterday, officials at the Grand Union Basics store pointed out the differences in their prices and the averages they said were charged by competing supermarkets in that area.

Examples included Briggs bacon, 99 cents a pound at Basics, compared with 1.47 at other stores: Coca-Cola, $1.35 for a six pack, compared with 1.99 at other stores, and Dannon yogurt, 2 cartons for 83 cents, compared with 96 cents elsewhere.

Grand Union officials said the new Basics store in Marlow Heights, will be open 24 hours a day. Other Basics stores operated by Grand Union are in Florida and New Jersey.