"There's a store out in Rockville selling dented cans with labels," said the voice on the other end of the phone. "Is that legal?"

Absolutely, according to the Montgomery County Department of Environmental Services; as long as certain regulations are observed, regulations that are meant to protect the public from unsafe food. And the 23-year-old entrepreneur who sells the dented cans at the Discount Food Outlet at 1011 East Gude Dr. says he complies with those regulations because: "If I get anybody sick, there goes my business."

Frank Zoche's business is selling what is sometimes called salvage - not only slightly dented cans but crushed boxes, cans without labels and items boxed in bulk - all at greatly reduced prices. The merchandise may come from a bankruptcy sale, which case it isn't necessarily damaged. It may come from a manufacturer in a carton containing unlabeled cans, some of which are perfect, some of which have salvagable dents, some of which must be destroyed. Not all dents are acceptable. It is Zoche's ultimate responsibility to sort the merchandise to make certain only perfectly safe foods are sold.

The sheet of information Zoche hands each new customer at his 2-month-old store explains his operation: "We buy our stock from trucking lines, railroad freight, bankruptcy sales, auctions, food chains, and direct from manufacturers. Some cans are dented, and some boxes are crushed, but the contents are perfect. (We comply with all State and Federal health codes in regards to dents.)

"If you don't mind buying dents you can save a lot of money. All contents in dented cans are just as fresh as your neighborhood grocers, and all dents last just as long on your pantry shelf as non-dents."

How does Zoche know the food is not old? Because he can read many of the code dates stamped on the products.

Cans without labels can be sold only by the case. By law a label must be attached to the case stating the contents and distributor. The label also says: "Warning, the enclosed items are to be sold by sealed case only. Any individual unit sale of the contents of this case is in violation of federal and state law."

So far Zoche's business has been good. What he has to offer is much less expensive than in the supermarket: a 1-pound box of Hungry Jack mashed potatoes (slightly crushed, but still completely sealed) was 79 cents, 20 cents less than in supermarket; a 32-once box of Carolina extra long grain rice was 61 cents or 18 cents cheper; an 8-ounce jar of Hellman's mayonnaise cost 45 instead of 53 cents; 14 ounces of Del Monte catsup was 47 instead of 59 cents; a 32-ounce jar of Heinz white vinegar cost 45 instead of 55 cents; a 16-ounce box of Post 40 per cent Bran Flakes was 60 cents instead of 83; 16-once jars of Greenwood red cabbage were 30 cents each, 4 for $1 instead of 55 cents.

Those who buy in large quantities - either because they have large families, buy with others or belong to a food co-op - will find the greatest choice and the cheapest prices. The savings on a 24-jar case of the cabbage was $4.56, making each jar only 19 cents. Six 10-pound bags of Uncle Ben's converted rice was $15 or 25 cents a pound, which is about half at the supermarket.A 20-pound box of San Giorgio pasta cost $3.80

Zoche says he does half his business selling to wholesalers, the other half at the retail level. He got into discounting because his father, who runs a similar business in Florida, suggested it when Zoche needed a job. "The company I worked for," Zoche explained quite candidly, "fired me, so my father said why don't you do it." Zoche thought it might not be a bad idea, especially since he doesn't "like working for other people. But my friends said I was crazy and my wife said 'no, we'd better not.'"

Zoche wishes now that he had been better capitalized when he started and admits he hasn't shown a profit yet, though two months is probably too soon to tell.

He's optimistic, however. He's says he's got a terrific location - a high traffic area with two discount bread store, discount tire and carpet shops, a place to buy day-old donuts at reduced prices and a shop where used appliances are reconditioned and sold with a year's guarantee.

His biggest problem at this point is not lack of customers but satisfying them. He doesn't have sufficient merchandise and good-naturedly admits: "I went into this thing before I had enough stuff for the public, before I had enough sources. They'd buy more if I had more."

For those who want to purchase salvage merchandise, or pick up a reduced-price dented can in a regular supermarket, watch out for certain things.

Don't buy any unlabelled cans unless they come in a sealed carton and carry the warning label required by the government.

Don't buy cans which are dented on the rim or the seam.

If a dent is severe enough to make the can bend in the middle, leave it in the store.

If the can bulges anywhere, sides, or ends, it probably contains gas, a sure sign the contents are spoiled, or worse, poisonous. When such a bulge is pressed in, it usually clicks when released.

Keep away from boxed goods if the inner seal is broken in any way.

Vacuum packed jars should emit a slight noise (the air escaping) when they are opened. If they don't, discard the contents.