Saturday morning, Kevin and Alan Gowen will hook antisnooze beepers over their ears and climb into the black Jeep Cherokee they have outfitted with a time-speed-distance computer, a stereo system and a bunk. Kevin Gowen will say a prayer against motion sickness.

Then the brothers, natives of Bethesda, will begin a journey of 8,230 miles around the perimeter of the United States -- in eight days. Call it adventure, call it a lark, but most of all call it an endurance test -- a case, in the lingo of the long-distance driver, of "mind over bladder."

The Gowens are one of 130 teams participating in the third annual Uniroyal One Lap of America, a road rally that begins and ends in Detroit.

"We've always been interested in things automotive," said Kevin Gowen, 33, a vice president at B.F. Saul Mortgage Co. in Chevy Chase. " . . . We thought, 'What the heck?' "

The event, which is technically not a race, is descended from the infamous "Cannonball Run," the pell-mell coast-to-coast dash memorialized in two Burt Reynolds movies. Both the high-speed, controversial Cannonball, which ran five times between 1971 and 1979, and the legally sanctioned One Lap were created by Brock Yates, an editor at Car & Driver magazine.

In the One Lap, where the estimated average speed is 48 miles an hour, the object is to reach a series of secret checkpoints with split-second timing.

At the start of each leg of the course, contestants are given a set of complicated directions on how to reach their next checkpoint, excluding route numbers and road names. They are scored according to how closely they hit their designated arrival times; a team arriving five minutes early at a checkpoint, for example, is penalized five times as much as team arriving one minute late.

What's more, the route is expected to follow interstate highways and secondary roads. Thus, the participants not only have to worry about gas and restroom stops, breakdowns, hygiene, the potential discomfort of burgers-on-the-run and weariness, but also the possibility of, say, a lumbering school bus suddenly materializing in front of them on a two-lane road with no passing. The winner is the team with the fewest points. The grand prize is $10,000.

But the Gowens, whose previous experience has been limited to short local rallies, aren't in the One Lap for the money. They estimate that they have spent about $5,000 in preparations alone, including the $1,000 entry fee and $800 for the special rally computer that mounts on the dashboard and will calculate their movements around the country.

No, they entered the One Lap because they wanted to, because of its Walter Mitty, anybody-can-do-it appeal. "For the fun of it," said Alan Gowen, 36, a bearded father of two who has a general contracting firm in Carroll County.

"Because it's there," said Kevin Gowen, who lives in the District.

The Gowens see themselves as true underdogs. Not only are they unknowns, they are also operating under a numbers disadvantage. Most teams consist of three members, so that one person can sleep while the other two navigate and drive. But the Gowens opted for the two-person team, meaning sleepiness could become a weighty factor during their 168-hour marathon -- broken only by a 15-hour layover in Redondo Beach, Calif.

"If I'm driving, I can go 36 hours, get two hours sleep, and then I'm ready to go again," said Alan, the chief driver. His wife Pamela gave each of them a device that resembles a hearing aid and makes a high-pitched beeping sound should they fall asleep.

The Gowens also realize that being cooped up together in a jeep for eight days in a pressure-packed situation could get a little wearing on the nerves.

"He tailgates," said Kevin, describing Alan's most annoying habit.

"He gets carsick," said Alan, returning the favor.

But when it's all over May 11, after the parades and the parties, the Gowen brothers say they will be in perfect agreement about their next activity.

"Sleep," they said in unison.