TWO YEARS AGO, Valerie Ellsworth didn't know what a triathlon was. Now she's training for one at Oxford, Maryland, this month -- 50 miles on a bike, 20 miles on foot and 2.4 miles in the Bay.

She doesn't care if she comes in last, which is a distinct possibility. She just wants to cross the finish line.

And what she'll do to get there is give up friends, relaxation, red meat and peanut M&Ms. Just like any other driven recreational athlete.

"It's fascinating to me," says Ellsworth, "pushing my body and seeing what it can take."

Their forces are growing, these impassioned individuals who found fitness and want to go further. They train, and, if they think it'll help, climb on treadmills to have their gait analyzed, stick their feet in plaster, dunk themselves in water tanks to be weighed, and talk it out with a sports psychologist. All in the name of maximum performance. Taking it to the max.

Although the triathlon comes close to the ultimate test of athletic mettle, it doesn't matter what sport it is. From softball to skating, enthusiasm and perfectionism are universals.

"It keeps me off the streets and out of the bars," says Ellsworth, 32, a personnel recruiter who says she hasn't had a mood swing in years. "I used to drink, smoke and play around a lot," she says, with the conviction and bubbliness of the born again.

It started in November 1983 when she joined the Tysons Corner Sporting Club with a friend. A former water girl on the college softball team, Ellsworth first tried aerobics classes. Then she overheard the sporting club's coach, Chip Hill, talking triathlon. "First he told me what it was," she says, "then he showed me."

Now she trains weekday evenings after work from 6 to 9:30, and all weekend long. Because she eats dinner on the drive to the club from her office in Rossly, her car is a bag lady's delight: fruit, cheese, plastic containers full of rice or noodles, bags of rice cakes, along with changes of clothes, curlers and makeup.

Her schedule, which Coach Hill pins up on the club's bulletin board, goes like this: On weekdays, running a loop, uphill and down, from five to eight miles; swimming two miles; and/or doing Nautilus, upper and lower body. Weekends are more rigorous: biking Saturday 30 to 50 miles followed by a few sets of tennis (the only sport she'd ever tried before the bug bit). Sundays she'll run 15 to 20 miles then jump into the pool for 2.4 miles.

"My weekends belong to my coach," she says, from coffee at 8 Saturday morning until 4 p.m. Sunday. "I don't party. I'm not a social individual any more. I feel guilty when I take a day off."

Men just have to understand these things about Ellsworth. Because they know dedication, she likes men who run their own businesses. (She's done that, too.)

Ellsworth is a marathoner by choice, with the triathlon merely a cross-training ground for that.

"It's just personal self-fulfillment," she says. "Every time I run I want to feel I ran better than I ever have before. Every day I can see what else I can do.

"It helps everything all around. Your runner's high? I am high all the time." And she projects her energy over the phone at work. "Even a bad day is to be chalked up -- hey, we're entitled to these," she says.

A turned knee kept Ellsworth out of a triathlon last year. With most athletic injuries coming from overuse, as a preventive measure Ellsworth puts orthotics in her running shoes (which are the most expensive shoes in her closet -- even without the $250 orthotics). "Biomechanical orthotic devices," as they're called, are prescription shoe inserts molded to fit the foot from plaster casts. By controlling abnormal motion and reducing jarring, they can lessen heel pain, knee pain, back pain, and worse.

Some marathoners swear by the for promoting good form, thus preventing injuries. As Annandale podiatrist Myles Schneider, who is also a runner, says, "If someone has inefficient biomechanics, their performance will be affected. If you're a runner and don't have good form, you'll fatigue easily and won't be as efficient as you should be."

Newlie Hewson, 62, is a national middle-distance champ who runs in every race he can from Raleigh to San Diego. He's tried orthotics; in fact, he'll try anything that sounds like it could shave off a few seconds, from carrot juice to carbo loading. At the moment, he's considering towing training, which he describes as water skiing minus the water and the skis. Instead of a boat, a jeepster pulls you along as you run behind it.

"You're extending your speed limits," says Hewson. "It's a new wrinkle. I'm really enthused about it, though it's a little on the dangerous side."

As a retired statistician, Hewson analyzes his performance ad infinitum. He keeps a log of his running where he records humidity, pollution and wind speed. "I have analyzed my total program and regimen," he says, "nutritionally, speed-work- wise, distance-wise."

Competition definitely improves his performance, he finds. As does the yoga he practices for relaxation -- which maybe he carries a little too far. "When I run," he says, "I feel like I am in a jungle hammock with my girlfriend giving me mint juleps. I only open my eyes as much as I have to, to keep from running into people."

When he measured his stride length and discovered it fell short of optimum, Hewson went to the Sports Medicine Center at Capitol Hill Hospital for a video analysis of his gait. As he ran on a treadmill, he was videotaped from the shoulders down, front and side views. Then he hopped off and watched himself in slo-mo. Silent running.

"It's looking at yourself and realizing that you're sloppier than you thought," he says. "The arm length, the stride length, the lateral motion if any. There are various aspects to smooth out so you are running as effortlessly as possible."

It's no substitute for a coach. "And we hope the coach isn't a sports medicine program, either," says Peter Sauer, the center's director. "We can coach you in a preventive way, but we can't stand on the track with you every day." The center has used video analysis on baseball pitchers, ballerinas, golfers, aerobic dancers, having them go through the motion of that particular sport to see what may be causing chronic pain.

"The thing we do best," says Sauer, "is keep the weekend warriors going."

In its "fitness consult," the center evaluates the diet and lifestyle of the out-of-shape. Beyond that, a "personal performance evaluation" tests to determine how long it takes to achieve your maximum heart rate, or go into oxygen debt, such states as are considered nirvana to Type-A athletes. If you're not fit, this sort of testing tells you where to start training. If you are, it may be something to brag about. Regardless, it establishes a baseline from which future testing would reveal if your training is working.

American University's Center for Health/Fitness does similar testing. "We are trying to help individuals maximize their potential to be healthy human beings," says director Bob Karch. "The first step is to have a person discover who they are physiologically. A 95 golf score is not so good; 75 is pretty good. But what's your score in cholesterol, what's your score in body fat, in triglycerides, in body strength and flexibility?" he asks.

Often people visit the center to supplement their annual physicals -- to develop an individualized exercise program. And for that they need to know how fat they are. The center offers one of the few "fun" lab tests -- a hydrostatic weighing tank. Instead of pinching your skinfolds with calipers to measure your body fat, a technician sits you in a cage attached to a scale and lowers you into a tank of water until you're completely submerged. Instead of holding your breath, you blow out as much air as you can. That weighs something too.

"Some people may be underweight but overfat," says Karch. "We look at what would be an acceptable percentage of body fat." For men, says Karch, it's 16 or 17 percent of the total weight, for women 24 or 25. Ideally, if you were fatter than you wanted to be, you'd go on a slow-paced diet; crash dieting depletes lean muscle mass, and you want to hold on to that.

"Lean is in," says Karch. "You couple that with the time spent developing your skill, chances are you're going to be more efficient. Well-developed musculature as well as an acceptable body fat translates into that fine-tuned racing machine."

But what about rust, corrosion, dead batteries . . . in short, the aging process? John Wilmeth, an outfielder in the local fast- pitch leagues, recently attended a clinic run by Bethesda sports psychologist Laura Hitchcock. Wilmeth, who plays softball three nights a week, came to the clinic because he wants to compensate mentally for his lessening performance physically.

"I am 36 and a half. I can see I can't run as well as I could," says Wilmeth, a financial analyst with the Small Business Administration. "The idea is to use any means to maximize my performance -- even though, over a period of time, it's a losing battle."

Hitchcock helps athletes find that mental edge, that competitive edge. One major success story is the teenage ice skater who not only achieved her highest skating tests with Hitchcock's help, but found her math improving too. Actually, Hitchcock's techniques for confidence building and relaxation "could be applied to anyone who's interested in performance," she says, including actors and sales people. Even a body builder has come to her: "They sculpt their bodies and project themselves," she says. "This guy would like to maximize his performance and really turn it on in front of the judges."

Wilmeth wanted to improve his batting average. Since the clinic, a few minutes before going to bat he's been using visual- motor behavior rehearsal: He pictures himself getting a good hit. And so far, he says, it's been working.

To practice this visual imagery, you need a little imagination: You're participant or spectator. You can picture yourself looking out at your own performance -- eyeing your landings for the triple jump, for instance. Or you can picture yourself at the plate through an overhead camera, or from the backstop, with the smell from the hotdog stand wafting past. Visualization should be practiced daily, says Hitchcock, using all the senses.

To learn a new skill, says Hitchcock, you need a model. A gymnast may see herself riding on Mary Lou Retton's back as she does the moves perfectly, or with her face on Retton's body.

It's all towards finding what psychologist Bruce Ogilvie, who worked with Olympic athletes in Los Angeles last year, calls the "flow state . . . the positive interaction of mind and body." It's giving your body permission to do its best.

Says Ellsworth, as she prepares for her triathlon, "It's 75 percent psychological, once you get over the level of fitness. It's a mental game. Your mind can bring you down at any time." Especially after the other marathoners hit the wall.

"My coach told me, 'The last five miles, don't look at anybody on the sidelines. They'll be in pain. If you start to empathize with them, you'll break your stride. You're finished.' "

What motivates people to seek their personal limits? The self-absorption seems to be the logical aftermath of the Me Decade. Karch says it's "a compulsive thing. Now they have an opportunity to shine or stand out in their age group or with their friends; they never had it before. But you have to ask yourself how much time can I afford personally to train, how much do I have left to spend with my family, social life, job?"

For Ellsworth, the answer is obvious: "I feel really good about what I am," she says. "Now I have direction. Every day is an absolute challenge."

SPORTS PSYCHOLOGY CLINICS -- with Laura Hitchcock. At First Class, 1522 Connecticut Avenue NW, June 26, 7 to 9; and July 24, 8:15-10:15. $10. To register, call 797-5102. And through Learning Works, June 13, 7 to 9, and July 11, 7 to 9. $15. To register, call 657-4488. For information on individual sessions, call Laura Hitchcock at the Sports Psychology Center, 656-7510.

NATIONAL CENTER FOR HEALTH/FITNESS -- Hydrostatic weighing, $40. The Human Performance Laboratory does a full range of physiological evaluations for $295 (cardiologist-supervised treadmill test, health profile questionnaire, blood profile, assessments of body composition, pulmonary function and strength and flexibility); a lesser menu costs $135. At American University, Massachusetts and Nebraska Avenues NW. Phone: 885-6275.

SPORTS MEDICINE CENTER -- Fitness consult, $35 (discussing eating patterns, exercise, personal outlook and goals). Videotaped gait analysis, $45 plus a $21 office fee. At Capitol Hill Hospital, 700 Constitution Avenue NE. Phone 269-8775.

RUNNER'S EVALUATION CLINIC -- Gait analysis with sports medicine specialist, June 15, 1 to 5. $20. At 3001 Audubon Terrace NW, through Open University. Call 966-9606.

FITNESS EVALUATION, and fitness program guidelines. Bethesda-Chevy Chase YMCA, 9401 Old Georgetown Road. Non-members, $30 for initial evaluation; $25 for reevaluation. Contact front desk receptionist, between 9 and noon, Monday through Friday, at 530-8500.

EXERCISE EVALUATION & CONSULTATION -- Testing body fat (skinfold test), flexibility, strength and endurance. Non-members, $25. National Capital YMCA, 17th and Rhode Island Avenue NW. Phone: 862-YMCA.

BODY ALIGNMENT IN ACTION -- Jogging clinic with emphasis on improving form. Session I: June 8 and 22, 10-12:15. Session II: July 9, 16 and 23, 6-7:30. Non-members, $46. National Capital YMCA, 17th and Rhode Island Avenue NW. Phone: 862-YMCA.