Q. My husband and I would like to begin an exercise program. Our problem is the same as many others, I'm sure. Limitations on time due to jobs and family responsibilities make it difficult to devote a large amount of time to exercise. How much time must we spend a week to become fit? Money constraints preclude joining a health club. Can you lay out a weekly regimen for the average person in each of the four fitness areas?

D. & J.R.

Leesburg.

A. Your question is a common one that unfortunately can't be answered in one column. There's just not enough space to give you all the information you'd need to organize an entire program for the four elements of fitness -- muscular fitness, cardiorespiratory fitness, flexibility and nutrition.

It's like asking Joe Gibbs for information about football so you can coach the local high school team, or an electrician for advice on how to rewire your home.

So I'll confine myself to answering your question on how much time to spend exercising each week. It depends on how fit you want to become. The intensity, duration and frequency of your exercise will dictate how fast and how much you improve. Many people want the best results possible but aren't willing to invest the time and energy needed to stimulate maximum gains.

Let's start with the minimum amount of time needed to generate physical improvement. Realize that these are opinions based upon my reading and my experience. Remember that for any type of exercise to be beneficial, it must be regular. Since these are minimums that I'm recommending, don't make any cuts. If you miss one session when you're using minimums, you'll regress physically. You begin to lose fitness approximately 72 hours after your last workout. On the other hand, don't worry that it will take longer to get results training at minimum levels. Be patient with your progress.

* Perform stretching exercises for a minimum of 30 minutes a week. I'd suggest three 10-minute sessions on alternating days. Do them any time that's convenient. Include a wide range of exercises designed to stretch each major muscle group. To minimize boredom, change the order and substitute different movements frequently. Maximum gains can be developed by stretching five to six times a week in 20-minute sessions. A sound book on stretching is Bob Anderson's "Stretching" (P.O. Box 2734, Fullerton CA 92633).

* The cardiorespiratory system can be improved with as few as two training sessions a week, preferably not in succession. Ideally, each workout should last at least 20 minutes. This does not include a warm-up or cool-down period, which would add about five minutes both before and after. Four training sessions a week of 30 to 45 minutes each will produce maximum CR benefits.

When you select an activity that fits your schedule, remember that it must involve the large muscle groups, be continuous and rhythmical, and sustain a heart rate of 70 to 85 percent of your maximum. The most effective activities available to you at home without buying any equipment are walking, jogging, running, aerobics and jumping rope. If you're willing to purchase a stationary bike or rowing machine, you'll add some variety.

Working out together may be a problem for you and your husband. If you choose jogging as your training mode, for example, you may not be able to run together at the same pace. You may be more fit than he or vice versa. You may have to jog at a rate of 10 minutes per mile to get your heart rate at 80 percent of maximum, while, because of his existing level of fitness, he should be jogging at a 12-minute pace.

In any case, a good book to read is Ken Cooper's "The Aerobics Program for Total Well-Bing (Bantam Books).

* Muscular fitness can be improved with two 20-eek. Maximum gains can be obtained with three 45- 60-minute workouts. A problem that you may encounter is equipment. If you have a barbell, you can organize a general overall program. Dumbbells or a home gym would add variety to the program.

I try to avoid plugging my own stuff, but in this situation there may not be a reasonable alternative. I've written four texts on strength training. Two of them would help you set up your program at home. The first, "Strength Training by the Experts," gives detailed instructions on organizing a program and photographs illustrating how to use a barbell, a dumbbell and a Universal Gym.

The second, "Maximum Muscular Fitness: Strength Training Without Equipment," provides instructions and photos on how to gain strength at home without the use of any equipment. The publisher is Leisure Press, Box 3, West Point NY 10996.

* Your nutritional n more common sense than anything. You've heard it before, but the general guidelines are: Eat a balanced diet from the four food groups; decrease sugar, salt and fat intake; increase fiber and carbohydrate intake.

How much time should you devote to your nutritional needs? Your entire lifetime. If you're trying to lose fat, do it sensibly; don't try losing more than two pounds a week.

So what is the minimum amount of time you can spend exercising each week and improve your fitness level? Let's add it up and find out. FLEXIBILITY

TIME 10 min/workout

FREQUENCY 3x/week

TOTAL CR FITNESS

TIME 30 min/workout

FREQUENCY 2x/week

TOTAL MUSCULAR FITNESS

TIME 30 min/workout

FREQUENCY 2x/week

TOTAL 60 Min COMBINED TOTAL 2 hrs. 30 min.

Your schedule or preference will dictate which activities you perform on any givn day. If you wish, you can perform everything on the same day. Your schedule would then be: Stretch, run and lift Monday/Thursday (or any combination of days allowing two days between workouts). Stretch once more on Saturday or Sunday.

If you wish, you can alternate your CR and strength workouts. Run on Monday and Thursday, lift on Tuesday and Friday. Stretch Monday, Thursday, Saturday. If weekends are the best time for you and your husband to exercise, use Saturday or Sunday for one of your exercise sessions. Then you'll only have to juggle your schedule once or twice during the week.

You'll only have to leave your house twice a week to run. If you use a stationary bike or rowing machine, you won't have to leave your house at all. When you analyze the above routine, it's almost impossible to find an excuse for not exercising -- unless you're satisfied with your current state of fitness (or lack of it) or too lazy to invest 21/2 hours a week to look and feel better. Add just another hour or so to that and you'd be investing enough time to stimulate near-maximum fitness.