THE IDEA IS ENTICING: "Use your drive time as fitness time."

Our streets and freeways have gotten busy enough to make many drivers lament the time lost. Now two audio tapes promise that you can exercise and reduce stress while driving.

Natalie Manor, who owns a marketing and PR firm in Merrimack, N.H., came up with the concept during commutes to Boston to visit a bedridden friend. While figuring out exercises for her friend, she wound up with KarKicks. The two-tape package uses music and Manor's narration to lead the driver though 14 (non-aerobic) movements, working from the neck to the knees.

I tried it and was sore the next day from the shoulder rolls alone. But as I was doing the neck stretches - right ear to right shoulder, left ear to left shoulder - while driving down I-5, I began to wonder about safety.

Manor says the tape has been endorsed by the New Hampshire Safety Council, and she includes safety reminders every 90 seconds or so: Keep one hand on the steering wheel at all times, do only the exercises you feel safe doing. But she also includes a disclaimer in case of accident.

So I arranged to listen to the tape with Trooper Rick Johnson of the Washington State Patrol. From the start Johnson, a three-year veteran on I-5, I-90 and I-405, was not keen for any kind of distraction from driving. "We have enough decisions to make when we aren't exercising," he said.

He didn't have a problem with the starting position, though: sitting up straight and holding in your stomach. I did: "I have a hard time remembering that" despite Manor's many reminders.

After a few minutes, I checked: "Are you holding in your stomach?"

"I can't help it," Johnson said, knocking on the bulletproof flak jacket under his uniform shirt. "These make you have good posture."

The "one hand on the steering wheel" reminders didn't impress him: "In driver's ed in this state, they teach us to keep two hands on the wheel." Even though two hands were on the steering wheel for shoulder rolls, Johnson didn't like the hands being pulled back. And when Manor described the neck stretches he said, "Oh my gosh - what if you want to change lanes, or someone else does? Your peripheral vision is gone on one side."

Two other exercises - holding out one fist and squeezing, and pushing up on the ceiling with one hand - could also block the driver's vision, he said.

As for the exercises that involved tensing the upper legs and buttocks, Johnson said, "I would love to know how they think you can control your vehicle doing that."

Still, the trooper was a trouper, even when we got to the Kegel exercises, and I had to explain what they were: "You know, uh . . . when you contract your pelvic muscles, um . . . like pregnant women practice?" For the record, he thought they were OK to do while driving.

Johnson thought that some of the exercises could be done safely, especially if practiced without the tape and don't feel rushed to keep up. Or if you were on such a desolate stretch you could employ cruise control. Most exercises could be used safely by passengers, he said, as long as they didn't impair the driver's vision. Some parents run the tapes to keep their children occupied while riding.

Manor didn't take issue with Johnson's concerns; she repeated that a driver should do only what feels safe and comfortable. But she did say the distraction level decreases with practice.

She has another tape for once we get to work, Desk Kicks. She's also planning an ergonomic health tape for the car. The sets are $14.95 each plus $3.25 shipping and handling (P.O. Box 1508, Merrimack, NH 03054; 1-800-666-2230).

I've been trying KarKicks in the stopped part of stop-and-go traffic. Manor still catches me with the part about holding in my stomach.

Maybe I should try one of those flak jackets.

-------- NOTEBOOK -------- Fitness news you can use

SINGERCISING To exercise your vocal cords while driving, local professional singer and coach Karen Oleson (448-0787) offers two tapes. "I'm Not Crazy . . . I'm Singercising" ($11.95) is a series of vocal warm-up exercises, and comes with a bumper sticker to explain your behavior to other drivers; "Singercise in Harmony" ($19.95) includes a book, taped instruction and karaoke-style sing-alongs. Singing isn't only for aspiring singers: Oleson says it can reduce stress, enhance moods and relieve depression. Tower Records on Mercer Street and Capitol Records carry the tapes.

EATING FOR IMMUNITY A study by the Department of Agriculture found that undereating can make the body more susceptible to infections. A group of Army Ranger trainees that had their calories cut by a third showed a 50 percent drop in their immune-system response. The group that ate enough to replace what they'd burned had a 150 to 200 percent increase in immune response.

AN ATHLETE'S FIT All that "generous-cut" clothing may not be what some fit men would rather wear. But guys with muscular chests, flat waists and developed thighs can have a hard time finding clothes that fit. The Built 2 Fit catalog specializes in those athletic builds, offering jeans, drawstring pants, shirts and accessories. 1-800-952-8458.

Molly Martin is assistant editor of Pacific. Write her at The Seattle Times, P.O. Box 70, Seattle, WA 98111 or e-mail mmar-new@seatimes.com