WANDERING about Harvard Square in search of cheap eats can be a demoralizing experience, especially for those afflicted with an acidic burning in the inner linings of their stomachs late at night. By now, even freshmen have learned that the Square's high rents mean places like Au Bon Pain can get away with charging you four bucks for a lame, lumpy and lazy sandwich.

Of course, seniors feel the most dissatisfaction, especially after eating at Elsie's or Tommy's for the last four years. Maybe that explains why my roommates have been popping Tums and Rolaids like Pez candy recently.

WITH this desert of fit desserts for hungry late-night studiers, one wonders why the arrival of Chicago Frank's to the Square has not received more acclaim. Snugly esconced in a white edifice at 8-1/2 Eliot Street, this small stand offers hot dogs that can drive aficionados into deliriums of appreciation.

"Some people come in here who haven't eaten a hot dog in 10 years, almost get down on their knees, and thank us for opening up," says Nick Lamberti, 34, who co-owns the store with fellow Boston College alumnus Tom Gianchristiano. They brought the Chicago dog concept from their Quincy restaurant, "Gianberti's," to the Square in July, soothing the hungers of hundreds of hot dog worshippers.

The object of this religious fervor is a creation which can only be described as a city-stand hot dog combined with a salad--it's called a "Chicago Hot Dog." A complex culinary concoction, a true Chicago dog must adhere to a stringent recipe, otherwise it will turn into a dripping, mushy mess.

You start with a kosher-style hot dog, sitting plumply in a steamed poppy-seed bun. The hot dog is not really kosher, but is all-beef with just a hint of garlic--all enclosed in a natural casing. It should come from the Vienna Beef Company of Chicago, if you are a hot dog purist.

Surround that with--yes, it's true--pickle relish, yellow mustard, a few chopped raw onions, a slice of tomato, a deli-style pickle and some nice burning jalapeno peppers, and you've got your dog. Chicago Frank's offers the dog for only $2.25, and if you use the $1 off coupons being distributed, that works out to the same price as five pinball games (for those of you figuring out opportunity costs). Also included are a handful of fries, hand-cut on the premises with the skin still on the ends, that make a mockery of the frozen icicles usually served in the Square.

Lamberti, found at 11:30 p.m. Saturday night steaming hot dogs at his stand, goes to great lengths to emphasize the legitimacy of his product, seldom found outside the Windy City. The two partners have toured the Vienna hot dog plant, sampled the wares of innumerable Chicago hot dog "restaurants" with names such as "Poochies," "Fatso's," "Bumpkin's" or "Herm's," and even worked a street stand to learn how the culinary creations are made.

NATURALLY, the variations on a hot dog are many, and Chicago Frank's seems to offer most of them. Beside the flagship dog are many other offerings: the Franko Bueno (a dog inside a tortilla shell with salsa and mozzarella cheese), the bagel dog (that's a hot dog wrapped in bagel dough), and the ever-present chili dog, corn dog and cheese dog. All were a delight to try, with the hot dog always superbly flavored and properly cooked, the toppings fresh and lively, and the fries crisply done to perfection.

This means paradise for hot dog lovers, their ranks decimated by all the "good health" crazes and concerns about red meat and cholesterol. But there are still some who proudly hold their hot dogs high, disdaining the trend-followers who crowd into Luscious Licks for their few globs of tasteless, technicolor frozen yogurt. "The problem with New Englanders is that they are very health-conscious, and don't eat a lot of hot dogs," says Lamberti.

For those who still shy from one of the world's finer pleasures (besides Grey Poupon mustard), Chicago Frank's also presents a wide lineup of other meals. Besides hot dogs, Lamberti and Gianchristiano also serve up hamburgers, various sausages, roast beef, chili, clam chowder, onion rings, and fried dough. These, unfortunately, were not up to par--it's obvious that Chicago Frank's is meant to do one thing, cook hot dogs, and nothing else.