It's a revved-up rally: circumnavigating US in taxis and pickups

BY the time the Minnesota truckers talk with us on the CB, we are little more than 24 hours out of Darien, Conn. The route is simple: the perimeter of the United States. The total distance is about 8,900 miles - although no one has told us for sure. We just follow our printed instructions and try not to add or lop off too many miles anywhere.

This road rally, called One Lap of America, began at 9 o'clock at night on Friday, April 13. We are due back in Darien tomorrow. That makes eight days on the road - seven days of driving, if you subtract the daylong layover here in Redondo Beach, Calif.

Seven days is 168 hours. An impossibly small time to circumnavigate the entire United States? If you divide 8,900 miles by 168 hours, you come up with an average 53 miles per hour - and the national speed limit is 55 m.p.h. The secret, as in all rallies, is to pace ourselves, keep up a good average, and follow the directions.

And that, says Brock Yates, event originator and a leading automotive journalist, is what separates a rally from a race - which this certainly is not. It's an endurance test, played out across the landscape of Interstates and truckers' radios, state troopers and rest areas, big Thermos bottles and the stark, almost eerie unpopulated hinterland of this vast continent.

This writer is teamed up with Brad Sears, a radio journalist and host of PBS television's ''Last Chance Garage.'' Our vehicle is a Mazda diesel mini-pickup with a home-brewed turbocharger that eats up mountain passes.

But if the kitchen sink had wheels, it, too, would be in this rally. Entrants include a luxury motor home and a Harley-Davidson motorcycle, as well as a propane-powered van, a couple of Porsche 930 Turbos, a pack of aging-but-still-proud muscle cars of the early '70s, and at least a half-dozen Saabs, one of which is driven by the head of the company's US operations, Robert J. Sinclair. A Lincoln Town Car is christened ''The Spirit of Charles Kuralt.'' And veteran drivers Parnelli Jones and Walker Evans are competing in a Dodge minivan.

It is clearly a different sort of event from the ''Cannonballs'' of the late 1960s and early '70s with which Mr. Yates was associated. There, the object was to leave New York, attain top speed as quickly as possible, and beat everyone else and your own good sense to Redondo Beach. The record for those illegal and unsanctioned races stands at just over 32 hours.

Today's decidedly more sedate event is supported by backers such as Car and Driver magazine, Chrysler Corporation, and many others. Race or no race, however , a certain raffish air pervades the rally. Among the drivers are both the tweed-cap-and-cashmere enthusiasts and those whose trademarks are bright nylon windbreakers. A crew from Waitsfield and Warren, Vt., calls itself ''the Holstein Racing Team'': Its logo is the familiar black-and-white mainstay of Vermont agriculture.

A cabdriver from Indiana is doing the course in a new Chevy taxi - complete with a pizza-company ad on the trunk and a running meter that tallied, as of Redondo Beach, a fare of some $5,000. The cabbie was stopped in Illinois as a stolen-cab suspect. There are Caddies and BMWs, MG replica-kit cars and Continental Mark VIIs.

Diverse as the vehicles and drivers are, everyone who started made it at least to the West Coast. Whether they make it back to Darien, however, is less important than when they make it.

The route will take them from southern California to Miami and then up the East Coast to Darien. The target for arrival at the finish line is the exact moment the team left, plus eight days - and the closer the better. That and elapsed distance determine the winner. So the lap, in addition to testing drivers' endurance, tests the ability of participants to calculate distances and times - and, frequently via dashboard computers, to put these computations in the service of the clock.

There are, of course, different approaches to how this ought to be done. A minimum of two and a maximum of four drivers are allowed. The only rule for vehicles is that they be in safe running condition. That requirement met, speeds and layover times become matters of personal choice.

Two-seater sport cars make terrible campers, so the inducement for their drivers is to play a little bit faster and looser with the speed laws to find lodgings for the night.

But if you happen to have entered a luxury car with a big back seat - or better yet a wagon, truck, or recreational vehicle with real beds - a 24-hour driving schedule becomes more realistic, and your average speed can afford to drop off. Our truck is equipped with a cap, a cooler, and a foam mattress, all accessible from the cab via a crawl-through window in the back. We've been on the road almost constantly - although the cooler has been neglected in favor of speedy truck-stop breakfasts.

We're not so much traveling as living in small capsules hurtling around America. And despite infrequent reports of near-mutiny in some crews, we are getting along remarkably well with our teammates and our competitors.

In this rally, no car is an island: All seem to have CB radios. Serving not only to bring in the truckers (so far a friendly lot), they also reproduce the feeling of being in a tree house: We are like so many kids with tin cans and resined cords, keeping one another awake and amused with stories of what happened on the highway last night - or on some road in New Jersey 20 years ago.

The CB has its practical side, too. It allows us to explain to the car behind us, for example, what was happening when we lost power heading downhill into Billings, Mont. An electrical failure cost us three hours and a fuel-injection pump - and nearly the whole rally - when a relay caught fire just as we were getting under way again. As it turned out, the worst of it was having the information in our dashboard computers accidentally dumped during the repair job.

One casualty of this kind of driving is the notion of separate days, divided by concurrent periods of darkness and rest. Any sense of yesterday or last night , or even something as simple as ''earlier today,'' is lost. You wind up with an 168-hour day.

And if differences between times of day become meaningless, so do differences between places. Yet you do learn a few things - like the inexplicable profusion of shops selling suntan products along a short stretch of Route 12 in southern Michigan, or that the Interstate Highway System in the intermountain West is showing signs of late middle age.

And there are lovely moments as well - like the full moon riding a bank of luminous clouds above Washington State, or sunrise on an overlook above the Columbia River. Those are the times when you take your tired eyes off the clock and computers and white lines before you.

With One Lap of America almost over now, the talk about next year has already begun. Many of us will be happy to do it again - and the field will no doubt be swelled by some who have heard about it along the way. One, a trucker we talked to in Minnesota who goes by the name of Nightmare, made a serious inquiry over the CB about entering his semitrailer in the 1985 event.

Let's hope he does - he really knows his way through Minneapolis.