At a desk in a small inner office, separated by an Indian bedspread from several women stapling anti-shoplifting security discs to patterned sweaters, Sydney Lewis, 32 entrepreneur, student of economics and owner of The General Store works with a calculator.

It's a 100-plus degree afternoon in Adams-Morgan, but the 48-car parking lot that Lewis acquired a month ago has been filled all day. Electric fans assist the meager air conditioning around 30 curtain-front dressing rooms where customers are lined up waiting to try on garments.

Lewis has plenty to calculate.

Earlier this month, the no-frills, cash-only store sold more than 1,200 sundresses, 6,000 T-shirts and 4,000 pairs of jeans in one week - six times the business a department store of equal size could hope for.

The formula is simple, yet Lewis is almost alone in this area in this style of doing business. He sells first-quality name brand items (Lewis, Bass, Danskin) - cheap. He does it by buying in huge quantities - as many as 25,000 sundresses at a clip - which encourages some manufacturers to sell to him at drastically reduced prices.

It's not such a wild idea for a former graduate student in economics whose thesis, so to speak, is to "show my friends that someone acting in his self-interest can provide a community service."

If Lewis hadn's thought of it himself, he had the best possible model to imitate - his father's hugely successful Best Products Co., Inc., the national chain of discount catalog stores. Founded 20 years ago by Sydney Lewis Sr., Best Last year pushed beyond $400 million in sales.

Sydney the elder, a wealthy Richmond philanthropist, political contributor and collector of Modern paintings sculpture and art deco furniture, has visited the General Store and likes it, his son says.And the father, although he doesn't like to reporters, can't resist a hint at the great admiration he holds for his son.

Sydney Lewis Jr. - who dropped the "Jr." about seven years ago because, he says, it makes check signing easier - rarely consults his father about business matters. "He's a very important person. I just wouldn't bother him," is how he puts it. But he does frequently call his younger brother Andrew, 31, now president of Best.

"We talk a couple of times a week. But he uses me as a sounding board and then takes his own advice," says Andy, who also has ventured north from Best's Richmond headquarters to visit the store and says he buys all his jeans there.

It never occurred to Sydney to go into his father's business. Quite the opposite. As a doctoral student at MIT. in the mid to late '60s, he was caught up in the anti-establishment tenor of the times ("We were all radicals then," he says) and was typically anti-business."I felt then they were exploiting labor and the whole trip. My father included," says Lewis.

He passed his PhD. exams, taught macroleconomics (the board view of the economy) for two years at MIT. then "walked out in a huff and puff," he remembers, without a doctoral degree. "I'm not that interested in practice."

With the $3,000 he had saved from teaching, he set off in a homemade camper, lived for a while in Detroit and San Francisco, everywhere, he says, not doing much, "just bumming around."

In 1972 he came to Washington, still disenchanted, still unsure of what he wanted to do. Through a friend he met Michael Willis, and the two decided to go into busines. Willis had started the Bong Works, a head shop, and with the help of some Thai friends, Willis and Lewis started making bongs, the pipes used for smoking marijuana.

Using money earned in the stock market, Lewis bought out Hoffman's furniture, a warehouse-like building chock full of second-hand furniture near 18th Street and Columbia Road. His strategy was to sell the furniture, move in The Bong Works and carry on his partnership with Willis.

Only the furniture didn't sell ("I soon realized that you had to be a special kind of person to sell a $1,000 couch") and neither did the bongs.

After five months, Willis and Lewis, who are still good friends, split up. "It was obvious that what was needed was good hard work and I was the guy who was going to have to do it."

Lewis regeared the shop as a general store, including the furniture. He kept items from the head shop, and added dashikis and long robes he had made locally. "As dumb as I am, I noticed that what sold fastest were the Indian and Mexican clothes ordered from the back of catalogs for headshop items." Before long, he was selling off the other items as fast as he could, and was into the clothing business called The General Store.

He does his buying by intuition. When he makes a bad choice, he simply marks it down, below cost if necessary, "I don't want it to sit on the rack and embarrass me," he says.

Anyway, he adds, "I wouldn't be out here selling at full price. Anyone can do that. I wouldn't feel I was doing anything." For Lewis, "doing something" is saving his customers money, employing 50 neighborhood people and making money for himself.

He says he's not sure how much profit he's making. Last year it was $38,000. He kept $10,000 to live on and put the rest back into the business. He lives in a one-bedroom apartment nearby and walks to work.

Most days he starts at 2 in the morning replenishing his stock from the warehouse across the street. He seldom leaves the store before it closes for the day. "A man wants to have a challenge, but at the same time I can see myself becoming something I don't want to be," he says. "My social life is zero and people relate to me only in this role." He skipped his brother's wedding last week, and worked instead. "It was his second time. I was there at the first," he says.

Lewis says when he's 35, he'll walk away from the store for good. He wants to get another camper, a little better one than he had the last time, and bum around the country for a couple of years.

After that, Lewis figures, it'll be time to get back down to business.