"Ready, when you are, Ace." Cheryl Rosen, sitting in the driver's seat next to me, hunched over the steering wheel and zipped down Leesburg Pike - at a cool twenty-two miles per hour.

Stodgy station wagons and sedans passed in the lane next to us, their drivers peering at us dawdlers. But there was a reason why we braved the dirty looks of our fellow motorists and drove so slowly. The rallymaster had said to.

The rallymaster had said a lot of things. Five hours, 100.72 miles and 109 road directions worth of things, as a matter of fact. We and 262 other people (in 131 other cars) wound through the back roads and byways of Loudoun County on a "Time-Speed-Distance" rally sponsored by the Washington Rally Club. Each car had a driver, a navigator and a five-page sheet of road instructions that someone called the rallymaster had drawn up. The trick, near as I could tell, was that the rallymaster had reached certain points on this meandering route at certain times - and we had to reach those same points in the same amount of time. We would be penalized if we arrived at checkpoints along the way earlier or later than the rallymaster had. I'm not talking about arriving two minutes early or three minutes late. I'm talking about people who win rallies that are hundreds of miles long by a few hundredths of a minute.

"It's a mental challenge, a logic game," says Jack Fawsett, an auditor for the Army who has rallied since 1963. "These guys who make up the rallies around Washington are friends of mine and, believe me, they can be devilish if they want to be." So you get up at an ungodly hour on a Sunday morning, pump coffee into you system, fill up the gas tank and spend the day in you car just to outwit some prankster? Us against him (or her)? Well, not entirely. According to Fawsett, the aim is as much to test one's own prowess in thinking quickly and in making minute-by-minute decisions.

Others have more limited goals. "I could care less about winning," notes David Sattler of Adelphi, who started rallying last October with a friend. "I see places I normally wouldn't see, things like weird corner stores that remind you of Ohio at the turn of the century. And it's a great excuse to bash around in the country for a few hours."

Bash around we did, at the mercy of the instructions I barked to Cheryl. "We have to pass a sign that says 'Difficult Run,'" I ordered.

"That's a dumb direction," she muttered. "We could be in New York by now." A glance at the watch I was using in a futile attempt to make calculations convinced me she was incorrect.

"No, probably only northern New Jersey," I said encouragingly. Easy for me to say - I wasn't driving.

As navigator I had to calculate how much time we should take to get from point to point and to make allowances for the difference, however slight, between the odometer reading of the rallymaster's car and of Cheryl's. "It's as easy as balancing a checkbook," someone called out to me gaily a few minutes before the start. No wonder I had difficulty.

I found it hard to keep my mind on the course and, as a math-phobe, to subtract under pressure. The driver had other concerns. CONTINUED ON PAGE 6, FROM PAGE 1. "We're in trouble ig we get a flat tire," Cheryl confided at Mile 1,.22 as we started up a treacherous-looking hill "I don't have a spare."

But we didn't blow out and we got lost only once.

"You did see the Kashway store sign we were supposed to pass, by the way?" I asked a little anxiously as we toddled down still another country road. According to the instructions we would find Route 7 4.26 miles after that sign. "I think we should have passed Route 7 about three-tenths of a mile ago."

"No, I figured you saw the sign." Think fast - you can turn around right then and there or hold your breath and go a little farther, hoping you just read the odometer wrong. We did both: First we went a little farther, then we realized we had better backtrack to the last place we'd turned. There went ten minutes, we sighed. And there went a Fiat with a rally sticker on its windshield, making the same mistake we did. That made us feel better instantly. Heh, heh. Suckers love company.

Everyone has his or her favorite "boy-did-I-screw-up" story, and sages of winding up several counties away from the rest of the pack are not uncommon. Just as cowboys gather 'round the campfire sharing tall tales of near escapes, so the post-rally conversaions over beer have become almost ritualized.

"We didn't get lost today, but we did drive off the road once," admitted Mike Lye during one of these rehash sessions. His navigator, Michael Banton, just smiled. They've pulled through some tough times together and are still friends. Rallying compatibility means you're still talking to your partner after five hours of enforced togetherness in a car.

Picking a partner is serious stuff, especially if you plan on participating together regularly.

"I couldn't be in the same car with my wife," admits Sattler."We'd argue too much." Each competes with friends, and they compare notes at rally's end. "I've seen fist fights break out between a driver and a navigator, but the people who curse and get PO'd are probably having a grand time," he added. "Other people are as level-headed as computers."

Most rallyists work in jobs that require technical or analytical skills. "I think in numbers a lot," says Sattler's wife, Diane Reese, a computer analyst. "I enjoy playing with figures. Beside, I'm a compulsive list-maker's dream."

Sattler added, "A good rallyist needs a lot of patience, a good head for math, good eye-sight and a high tolerance for being frustrated." He thought a minute. "But then again, I don't embody any of these."

Initially, the challenge for Reese and Sattler was simply not to get lost. "But it gets boring after a while if that's all you're worrying about," concedes Reese. "Now I concentrate more on keeping close to the measured time."

Others are more trophy-oriented. According to Dick Lieberman, a former national champion who has participated in rallies that stretch on for days, "The people who stick with rallying are the people who win."

Most experts use dashboard computers to help them make their calculations, rather than relying on wristwatches and pocket calculators. "You program the designated rate of speed into the computer," Lieberman explained. "It tells you if you're even one-hundredth of a minute off the time of the rallymaster."

"There's a heated debate going on about those computers," noted Fawsett."The traps are getting harder and harder since we don't have to be concerned with our timing so much. But now some people are returning to the old way."

The Metropolitan Washington Council for Sports Car Clubs, which coordinates rallying and autocross activities for the area, has instituted different classes of competition based on equupment and expertise, so that cahmpions with complicated computers are not pitted directly against us beginners with watches.

By Mile 86.83 Cheryl and I couldn't wait to get out of the car. "I think I'm too active for this,"said Cheryl. "I can't stand to sit in a car this long and just drive in circles."

A real rallyist would disagree: "I forget I'm even in a car and just concentrate on the course," says Farwett. "The only time I was ever uncomfortable was on hot summer days before I air-conditioned my car." CAPTION: Illustration, no caption; Picture, ALTHOUGH SOME RALLYISTS USE MINIATURE DASHBOARD COMPUTERS, OTHERS STICK WITH THE TRADITIONAL STOPWATCH.