While Scarsdale dieters are picking at their spinach and grapefruit, there is another group of weight watchers in the Bronx adhering to a loose regimen of Twinkies, pasta and Fritos. They are the disciples of Richard Smith, the irrepressible guru of good taste -- in fact any taste -- who counsels his followers to "eat all you want yet never be hungry."

Smith, 38, developed his philosophy of eating when he was 3 and lives by the motto framed on his kitchen wall: "Sugar is your friend." It is hardly the axiom of a man likely to cozy up to mung beans and kelp, but it is part of the message in "The Bronx Diet" ("The Diet Sensation of an Entire Borough") and a far cry indeed from Scarsdale. A unique book on gastronomics, it urges readers to eat, eat, eat -- cellulite be damned.

Like a souffle amid the 3,000 diet books now glutting the market, Smith's creed is enjoy your food. Enjoy your companion's food. Eat at a comfortable pace -- never more than one utensil in your mouth at one time. And avoid any wine with a childproof cap.

In the Workman paperback, he dispenses aphorisms like gumdrops: "A Hostess Twinkie contains twice the restfulness as that found in a pound of calf's liver."

Or: "There's more than one way to skin a grapefruit, but who cares?"

He also offers:

Pertinent insight into the causes of overweight ("large skin" or "licking plates that don't belong to you, especially in restaurants") and underweight ("reluctance to swallow food" or "gullibility -- believing a recipe when it says 'serves two.'")

Symptoms of underweight ("slide through bench slats") and overweight ("bend seesaws" or "hide cookies in the folds of your skin" or "rupture water beds").

Dangers of underweight ("getting lost in elevators," "inability to leave footprints," "chickenesque appearance when naked").

He lists only one danger of overweight: "Silly bowel movements."

Smith's first best seller, "The Dieter's Guide to Weight Loss During Sex," made puree of all the diets, trends and love-yourself manuals spawned by the self-help '70s. He manages to bring the same perverted insight and acute silliness to his second book.

Ripping off phrenologists with a study of reflexology, for example, he diagrams the areas of the tongue responsible for "less guilt," "getting act together," and "refreshing naps." Taking a jab at vitamin freaks, he prescribes riboflavin to "repel gypsies and aluminum siding salesmen, and to help you cope with est graduates" and plutonium to "survive unexpected visits from neighbors and the Welcome Wagon."

The author is an admitted foodfetishist. His passion for the stuff surfaced at the age of 2 when he discovered cake. In fact, he says with mock gravity, his earliest memory is of slapping together a sandwich made with pound cake and pumpernickel bread.

"I come from a Jewish family of eaters and built up my stamina by living in the Catskills for 18 years," he says.

Funny he doesn't look outstanding. He is a large man with a bald, mangoshaped head. And with his sad, sleepy brown eyes, he actually has the sombre countenance of a dietician or podiatrist -- not someone who breaks up at the mention of "kohlrabi" or flanken." Soul of a Silly Man

Only when he smiles does Smith reveal the soul of a silly man. This is not an insult. To Smith silliness is the highest form of humor. "I love silly. I think silly people are the best in the world," he says.

It was his solid caloric upbringing that laid the foundation for Smith's instant rapport with anything edible. "The first time I tasted pizza, it was like the moment Sutter saw gold or Columbus discovered America," he says. "My body needed no training to get used to pizza immediately."

His is, indeed, the Profile of a Well-Adjusted Eater as the book pronounces: "Eats between snacks... Enjoys airline food, even on the ground... Eats salads and okra only by mistake... Refuses additional helpings only when there aren't any..."

And what his is not is the Profile of a Maladjusted Dieter: "Treats food as a nutrition object... Defaces ketone sticks... Counts bites (difficult to do when drinking milk)... Puts in the month those things that are better left in the ground: celery, lettuce, roots and mineral water... Thinks thin (good only for those with a narrow head)."

Little League, bicycles and Cub Scouts mark most childhood memories. Smith's youthful milestones, however, are glazed with matzo balls, potato pancakes and apple studel.

"One of my favorite memories is watching the kitchen staff at my parents' resort roll out long tables of strudel dough," he says. "Being the owner's son meant I could cut off a foot-long piece of the freshly baked strudel, run off to the woods and eat it. It was wonderful. I think it was pre-sexual gratification."

Life in the Catskills wasn't all borscht and blintzes for Smith, however. As a waiter in a neighboring resort, he needed more than a soupcon of cunning to be able to eat on the job. He quickly learned to order 19 steaks for 18 guests, for example, then roll up the leftover piece and ingest it like a popsicle.

When there were cherry tarts for dessert, Smith found the easiest way to make contact with one was to drop it to the floor, bend down, shove it in his mouth, and let gravity take its course. "I learned to savor food instantly and get my lips around anything the size of a birthday cake," he says.

Although Smith's tastes range from cold meatloaf to caviar, he is finicky about the places he eats.

Restaurants with "organic," "beef 'n'" or "health" in their names, for example, serve too much salad and not enough bulk to suit his taste. Places with tablecloths or dress codes are too pretentious and pricey.And eateries that serve dainty portions -- like most French restaurants -- leave him craving hot pastrami sandwiches.

Worse, bistros with hanging asparagus ferns and highly polished wooden floors are dishonest. "They are for mentally imbalanced people," he grumbles, and are likely to serve two of the substances he most loathes -- kelp and yogurt.

A New York restaurant with none of the above is about as easy to find as oysters in August. But mercifully, Smith has found a Manhattan pizzeria where the scarred Formica tables are unsullied by cloths, the waiters wear thongs and the screaming sounds from the jukebox are likely to intimidate any living plant. If there are dress codes, they condone Smith's baggy blue jeans, plaid flannel shirt and fire-engine red suspenders.

Smith claims he has enjoyed 157 of his 158 meals at this find of finds. (The one exception was when he stayed home one night and whipped up his own concoction of black beans blanketed in melted Jarlsberg cheese and lots of cumin.) Because he has promised the owner anonymity, he will only reveal that it is within a 20-mile radius of a well-known midtown-Manhattan hardware store.

Although he has committed the menu to memory, Smith studies the list like the face of a dear old friend and orders his favorite -- linguine with red clam sauce, cold antipasto, garlic bread and a bottle of beer. The Sound of Spaghetti

When the steaming pasta arrives, he holds it to his ear like a conch shell and sighs. "Listen to that spaghetti. You can hear the sounds of Italy -- operas, men shuffling down the street." It seems to be his way of acknowledging that his food mania, like everything else about him, is part serious, part shtick.

How did Richard Smith get the way he is?

While lovingly wrapping strands of linguine around his fork, he unfolds a life story as whacky as one of his books.

When he was 18, he got a job driving a Pepsi delivery truck. His own airhorn, plus all the free soda he could drink, distinguishes his first job as the high point in Smith's professional life. He then went to Orange County Community College in upstate New York, but flunked out after failing gym twice.

Eventually he came to Manhattan, where he improbably landed a job as buyer of ladies' underwear for Alexanders' Department Store. "I hated it," he confesses. "I don't even like fabric."

Smith traded underwear for high finance and got a job checking letters of credit for Barclay's Bank. That was all right for two years because, he explains, there was a diner around the corner that sold veal parmigiana hero sandwiches for $1.50. His next job, as a tax accountant, lasted only six months. He quit when income tax time rolled around.

Smith used some of his Catskill cunning to land his next position. "I ripped out a bunch of fashion ads from magazines, put them in a leather portfolio and told Montgomery Ward I wrote them." He claims the department store believed him and hired him on the spot.

"There's nothing to that stuff," says Smith, feeling no remorse. "Anyone can write, 'Bartack's overalls will fit any man. They last for many years no matter how rough your sheep are.'"

His next job was writing press releases for the menswear industry. When his secretary's sister -- a literary agent -- read some of his spoofs on men's fashion, she urged him to try his hand at humor. Travel and Leisure magazine paid $750 for his first effort, "A Gentleman's Guide to Appalachian Wine Drinking." And yet another new career began.

On his 34th birthday, Smith quit churning out releases to become a full-time writer, and within two years sold his first book.

For the past two years, he has made his living parodying the things that most people regard earnestly. His first book sold 400,000 copies to readers who paid $2.95 to find out facts like making love to bread burns five calories, damp-mopping each other burns 10 calories and making love back-to-back burns 749.

To Smith, writing this stuff comes as close to nirvana as driving a Pepsi truck. "Nothing is more fun than getting paid to write about the things I know in my heart to be funny -- like bowling, est and flavor-enhancers," he says laughing. And nothing tickles him quite so much as when someone mistakes his falderal for fact.

"One sex therapist wrote me a letter saying she found my book the most enlightening sex manual on the market -- especially when I got down to the nitty gritty," he recalls. And several readers sent him letters claiming they had tried making love back-to-back -- and couldn't quite work it out.

As the author's fame continues to grow, the regimen of being Richard Smith becomes increasingly strenuous -- talk show appearances, posters, and calendars. He must jog 50 miles a week in Central Park to keep his 6-foot-1 frame down to a svelte 195.

He keeps a meticulous schedule. It's up by 8, write till noon, jog, shower and rest. He is unfailingly refreshed in time to catch "Tom and Jerry" at 4:30, "Our Gang" at 5, and "Uncle Floyd," (a kids' show out of Hoboken, N.J.) at 6 p.m.

He also reads A.J. Liebling, watches as many Mel Brooks films as possible and continues to avoid bean sprouts, discos and people with cameras around their necks. And at all costs, he stays clear of self-knowledge. "The worst thing that can happen is trying to make contact with your inner self," he says. "All you finally end up doing is poking holes in your major organs."