The metropolitan area has its first nofrills discount grocery store.

Careful shoppers, who prefer to buy name-brand merchandise, can save an average of 20 percent over prices at the regular supermarket on 300 to 400 nonperishables at Bag 'N Box, 8541 Piney Branch Road in Takoma Park.

Typical of the no-frills warehouse stores that have opened across the country over the last several years, the decor is "plain pipe rack" with merchandise stacked in boxes on shelves and on the floor. It is closed Sunday and Monday and has limited hours the rest of the week. There is no check cashing, though food stamps are accepted. Lack of fancy decor, of refrigeration and of other amenities also help keep operating costs down.

While the store supplied bags for the first few weeks -- "until people got used to it" -- customers will not only have to supply their own bags, but are expected to bag their own groceries.

Unlike some no-frills stores, individual items are price-marked. For those who want to comparison shop, the store has made it easy, providing a complete price list of every item it sells.

The no-frills store has been a long time in coming here, according to Don Maxson, sales manager of the parent company, M. Loeb Corp., "because people have been afraid of taking on Giant and Safeway."

Maxson described Washington "as among the most chain-dominated towns in this country." Safeway and Giant control more than 60 percent of the sales here.

Asked why his firm would go into a competitive business under the circumstances, Maxson said: "Because we have the least to lose." Loeb is part of a billion-dollar-a-year Canadian company, Pro Vigo. Maxon said, "Small independents have wanted to, but I've recommended that they not do it." He explained that they don't have warehouses and therefore can't make money at both retail and wholesale levels. A retail operation like a no-frills store, Maxson said, "wouldn't have the return on investment an independent would need if it were his only investment."

Asked how he thought Bag 'N Box would affect its nearest competitors, Pantry Pride and Giant, Maxson first said: "I hope a lot." But then he added, "Normally the supermarket closest to the box store increases business because you carry such a limited assortment."

Opening day, the Giant store manager across the street came to visit. Asked what Giant would do, Jerry Wade said: "No matter what happens, we have to remain competitive."

Does that mean meeting the prices at Bag 'N Box? Giant's house brands appear to cost eithr the same, a little more or a little less than the nationally advertised brands at the no-frills store. But for those who insist on name brands, there is a significant difference in price. On a 31-item shopping list of products chosen at random, the total cost at Giant was $44.52; at Bag 'N Box it was $37.37.