AFTER A steamy July day on the Ocean City beach, the only thing that tasted better than ice cream on a waffle was Thrasher's french fries.

All day long, lines of swimmers, sun worshippers and barefooted strollers would crowd in front of the stand across from the game centers anxiously waiting for the hard-working french fry men to dump basketsful of those tasty fries into huge cardboard buckets.

This truly good junk food, which was crisp-on-the-outside, mushy-on-the-inside, slightly sweet and greasy, was doused with, of course, apple cider vinegar and salt from over-sized shakers (for those who couldn't leave well enough alone). And it was dinner for many a high school fan.

When Thrasher's folded up its boardwalk location three years ago and moved inland to Baltimore's Harborplace, the crowd -- minus the sunburn and sand -- followed. But, come spring, Washingtonians can forget about driving up the Parkway for a french-fry thrill: Thrasher's is coming to M Street.

Although the opening date is not firm, Georgetown will soon be the new home of a second Thrasher's French Fries stand, according to owner David Brittingham. Now that he has the approval of Georgetown's three preservation committees, he is in the process of finding contractors to do the construction. The building and equipment will cost anywhere from $70,000 to $150,000.

"That's a lot of french fries," laughed the 32-year-old entrepreneur, an Eastern Shore native who looks more the beach boy than businessman. But turning out the Thrasher's french fry for the masses requires exacting standards and some heavy equipment: three custom-made deep fat fryers, an electric peeler/washer, an electric dicer and a sophisticated ventilation system.

It also requires a Western potato, which, he says, makes a crisper, prettier fry because it is drier, longer and slightly sweeter than its Eastern counterpart. In addition, the potato has to be durable enough to hold up to three deep fryings--the key to this french fry's success.

The Idaho is "the very best potato" because it's "the driest and not too sweet," Brittingham says. But since it's only available from January to July, the remainder of the year he buys his second choices: Oregon Russetts ("sweet and crisp") and California Long Whites ("very sweet, but not as crispy").

Brittingham should know about picking perfect potatoes; he's a potato peeler from way back. His apprenticeship began at age 17 in the Ocean City stand his uncle purchased from the original Mr. Thrasher back in 1953. During summers between college, where Brittingham majored in botany and plant genetics, he learned the business from the inside out. "I had no idea at the time I'd still be cooking french fries when I got out of college," he says. But when his uncle died in 1973, Brittingham took over Thrasher's.

For a few months, the young owner says he tried selling hamburgers and roast beef sandwiches along with his famous fries at a second stand in Salisbury, Md. But it didn't take long to realize that "over 60 percent" of his business was in french fries, and that the sandwiches on the menu were running up the cost "four or five" times that of the Ocean City stand, which only served french fries. He sold both the Ocean City and Salisbury stands and moved to Baltimore, where on a good day he'll go through two tons of potatoes, he reports.

The heavy equipment and tons of Idahos will soon arrive on M Street. But if you can't get to Baltimore and spring seems an eternity away, here are some of Brittingham's and other french fry experts' hints for making at home what have been called "very-close-to-Thrasher's-fries:"

Equipment: A large saucepan and fryer basket that fits tightly inside. Deep fat frying thermometer that clips onto the side of the pan.

Picking Potatoes: Select blemish-free Idaho or other western potatoes. Blemishes become ugly dark spots when they hit hot oil and, with french fries, esthetics do count. Check the potato for moisture by scratching a little skin off with a thumbnail and look for excess water. If it spits back at you, it won't make very crispy fries and should be stored in a dark dry spot, such as a basement, for about three weeks to dry out. In addition a damp potato can be a fire hazard--moisture causes hot oil to bubble up and it can go over the top of the pan onto the stove.

Preparing potatoes: If the potatoes seem somewhat soggy, soak them in ice water for an hour before cooking and you'll have a much crisper fry. Be sure to dry them very well. If wet when put in hot oil, the oil may bubble up over the top of the pan and, again, may cause a fire. Don't peel the end off, and leave a little skin on the sides when peeling. Skin adds flavor and texture. Do not salt before cooking. Wrap in slightly damp paper towels until ready to fry.

Oil: Use lots of fresh, high-quality vegetable oil. It's important that the oil be clean and unused because vegetable oil picks up the flavor of whatever you cook in it.

Deep-fat frying: Fill the pan with oil no more than four inches from the top of the pan to avoid bubbling over. The first fry of the triple-fry method cooks the potatos through; it takes about five minutes. The second frying firms them; it takes two to three minutes. These first two steps can be done up to two hours ahead of time. The third frying browns; it takes about two minutes. Shake the basket or poke the fries with a long-handled fork during each cooking stage to help keep the fries from sticking to one another. As they come out of the third frying, immediately sprinkle with salt and drain on paper towels.

DC FRIES (2 servings) 3 large, dry Idaho potatoes (substitute any western potato) 38-ounce bottle vegetable oil Salt

Wash potatoes. Peel, taking care to leave peels on ends and parts of sides. If soggy, soak in ice water for 1 hour, then pat dry. Fill a heavy pot 4 inches from the top with vegetable oil. Heat to 260 degrees on deep-frying thermometer. Put fries in basket and slowly lower into the hot oil. Be careful to watch bubbling oil so that it does not come up over the sides. Cook about 5 minutes, until fork slides easily into fry. Remember to shake basket from time to time to keep fries from sticking. Note: The fries still will be white. Remove and let oil drain back into pan.

Let oil continue to heat to 350 degrees. Lower fries into hot oil for second frying. This is the firming stage and takes about 2 minutes; shake from time to time to keep from sticking. When you lift them out of the oil, they will be only light brown. Fries can now sit up to two hours before beginning third frying.

Heat oil to 375 degrees. Slowly lower basket into oil. Cook about 2 minutes until dark brown (remember to shake the basket); remove from oil. Salt immediately and drain on paper towels.