Nelson Freck, District bookstore owner and adventurer, has devised an unusual way to travel this summer: cross country by bicycle. Although his idea is not unique, the way Freck plans to carry it out is as typical as a relaxing rush hour in Washington.

Freck, 36, will be one of 35 competitors in the sixth Race Across America (RAAM), at 3,100 miles the world's longest bicycle race and perhaps the toughest test of athletic endurance.

The race itself is simple. The riders will start Saturday in San Francisco and end up at the parking area on the Washington Monument side of Constitution Avenue between 15th and 16th streets NW.

That's where the simplicity ends: The winner is expected to finish within nine days. If that happens, the winner will have traveled about 350 miles a day, averaging about two hours of sleep each day. The competitors will eat while riding their bikes.

Promoters of the race picked Washington as the finishing point to heighten media attention. Last year's race ended in Atlantic City, N.J. This is also the first year a Washington resident will compete.

Despite being a rookie, Freck does not plan a leisurely trek across desert, mountains and plains. He expects to win. "Finishing is not the thing," Freck said. "It's how fast I can do it."

Considering Freck's riding past, it is understandable that his newest marathon venture worries him little. While in college, Freck decided to celebrate a new 10-speed bike by riding 160 miles in Illinois from his parents' house to the school he was attending. He started at 3 a.m. Sixteen hours later, he was a cycling veteran.

"After 20 miles, I realized it would probably be more than I could handle," Freck said. "I stopped every 10 miles to recuperate. I've never been in such pain."

But that was a mere jaunt compared with other trips. He's ridden from Washington to St. Augustine, Fla., and back. He's pedaled to Dallas, then on to Denver before returning to Washington, a 5,000-mile trip that took five weeks. He rode from the District to Canada and back in 29 days.

Freck graduated from American University in 1975 with an accounting degree, but opted for outdoor work as a bicycle courier. He was nicknamed "The Iron Man" for working under any conditions. After a few years he grew tired of the rain, snow and cold and wary of the hazards of his job. "I figured there's got to be a better way to make a living," he said.

His concerns proved prophetic. He suffered a broken leg, a concussion and a broken wrist when he was hit by a car while making a delivery. He sued the driver, won a settlement and opened a bookstore. "You don't need a whole lot of money to open a bookstore," he said.

The store, at 3512 Connecticut Ave. NW, specializes in science fiction and mystery books. Its name? Chaos Unlimited.

"I don't believe in doing what everybody else is doing," Freck said, sitting comfortably in the chaotic confines of his cramped store. "I've always wanted to do three things in my life: ride a bike cross country, own a bookstore and be president of the United States. But the last thing would be difficult because I don't want to start at the bottom."

Freck will need much guidance in his most trying venture. In past races, slightly more than half of the riders have finished. Only about one-third of the riders have been "official" finishers, arriving within two days of the winner. In 1985 a rider with no support crew was hit by a truck in the early morning darkness and is now a paraplegic.

Seven crew members will be the key to Freck's mere existence. They will exist in a family setting filled with fatigue and apprehension. They will live in a van and a mobile home, both donated by Freck's sponsor, Banner Life Insurance. They will cook, clean, chart times and plan schedules. But most important, they will be Freck's moral supporters.

"He's going to be out of his mind the whole time, so we've always got to be thinking ahead of the rider," said Jerome Kuh, the crew's mechanical chief. "If he's worried about us doing a good job, he's not going to be doing a good job. We've got to make sure he's drinking enough and eating enough so he can just go mindlessly cycling along."

Crew member Andrea Rebeck offered a less romantic observation about her job. "My biggest concern is that the place will smell like a locker room."

The prospect that the crew may get more tired than the rider during the race does not worry Freck. "I just ask that the crew keep me on the bike for 22 hours a day," he said.

Freck's cycling friends urged him to compete in the race after he completed a 300-mile ride in 21 hours in the spring of 1986. He trained hard for two months to prepare for a 700-mile RAAM qualifying race. He qualified by finishing fifth in that race in 45 hours, with no sleep.

"My strategy is steadiness," Freck said. "I have no speed." Freck plans to start RAAM slowly and catch the riders as they tire. He plans to sleep just 1 1/2 hours a day, and will take six-minute breaks every two to three hours.

Freck insists his success will depend on how he reacts when fatigue sets in. "At a certain point you get into a state where you don't get any more fatigued," he said. "I call it a Zen state. You focus on ride, ride, ride. The problem is, can you get along with not enough sleep?"

Is his wife surprised with Freck's latest pursuit? "No, not at all," said Kathie Freck. "It's just an extrapolation of everything he's done. One figures he's a grown man and he knows what he's doing. I've known him to do so many things with his bike that I'm not real frantic, but, of course, I do worry."

Is Freck himself worried? "I really don't have any {anxieties}," he said. "My worst fear is my opponents would be gods, and I just don't see that happening."