Even in the unpredictable Washington restaurant business, the success story of John C. Pyles III and Richard A. Stewart stands out as remarkable.

To begin with, the two men are unlikely looking restaurateurs, with their full beards, hair that falls below their shoulders, jeans and cowboy boots.They also neither do their own cooking nor stand at the doors of their restaurants gladhandling customers.

But they do almost everything behind the scenes, from designing and rebuilding the interiors of all four of their bar-restaurants themselves to ordering the lettuce and punching the adding machine.

And they make money. According to John Pyles, their flagship. The Greenery, on 18th Street NW near Connecticut Avenue, "does more volume than any place in Washington."

While such claims are impossible to verify, records show that Plyes' and Stewart's umbrella company - Restaurant Management, Inc., (RMI), which owns the Greenery, and the Paradise Cafe, Rocky Raccoon Saloon and PW's nearby - grossed about $5 million in 1976.

Pyles, 33, is a lawyer and financial consultant by training, and is president of RMI. Stewart, 30, is a former real estate excutive and RMI's vice president. But those are just titles. "We have equal ownership," Stewart said, "and we are the only ownership."

Pyles and Stewart began with a relatively small loan from Riggs National Bank, which they got after many refusals. They had trouble convincing local bankers they were serious about "getting dirty up to here rebuilding a restaurant," as Stewart put it.

What they set out to create, according to Pyles was "pretty good, total-environment saloons." They had no wish to create them as an adjunct their own social lives. "We're not some hippie-freak-wierdos," said Rick Stewart. "We're in this to make money."

Although they don't like it, their "total-environment saloons" are thought by many others to be like singles' bars. At all their places, strangers are seated together. At most of their places, a young crowd predominates. And no one has yet figured a way to keep the sexes from mixing with one another in such places.

Stewart insisted that RMI is not interested in "the groupie market." He said he has "always hated bars in Washington because everything is such a pressure cooker type of situation. We want comfort and comfortable people."

RMI's bar-restaurants serve medium-priced food and drinks and provide careful yet casual service, usually with college-age employees.

One carved-in-stone rule is that, on one's second visit to an RMI place, the bartender will greet you by your first name, without error. He will have introduced himself the same way, as will the waiter or waitress. And as long as you aren't too much of a caveman about it, employees will arrange introductions for you to attractive strangers.

The Greenery, easily the most distinctive of the four is filled - almost choked - with plants, and it is the only major downtown restaurant to feature seven vegetarian dishes on the dinner menu. The Greenery also offers, such novelties as cucumber sandwiches and, for dessert, yogurt. Its walls have lots of exposed brick, and its tables and bar are very light wood.

The effect is California. "There is still a newness to this idea on the East Coast," said Pyles, himself a vegetarian. "It's all a matter of presentation and quality control."

Around RMI itself, the mood is frenetic. The offices, in a dingy basement at 1829 M St., NW, can be found only because someone has taped a business card to the directory in the lobby. The reception room is always full of job applicants, and most the battered receptionist's desk is propped up on wooden blocks.

Pyles said RMI expects to remain small in terms of employees (it now has 425) and centralized in its management. But it is also lookint to expand nearby. That "is no accident," Pyles said. He called the area around Connecticut Avenue and K Street NW "the part of town where dense residential abuts a heavy commercial area."

The main problem at RMI, Pyles said, has been high turnover among middle management. "Some of our early people just weren't the right people," he said. "Washington has more nonprofessional restaurant people than anywhere else. Not unprofessional, nonprofessional. It's still a country town."

In addition to two new bar-restaurants planned for next summer, RMI is considering entry into the restaurant supply business. "Small restaurants have not made (suppliers) here be competitive," Pyles said.

Are Pyles and Stewart in danger of overextending themselves? "We're overextended what John and Rick should be doing, that's for sure," Pyles admitted. "But the key is doing it and not losing money or control. . .

We're going to mke a lot of people run for their money," he added. "We enjoy being competitive. We're far from our potential."