Most of us on vacation tend to be self-indulgent, giving in to every whim -- or at least every ice cream cone -- we can afford. But that's not the case on a weight-loss or fitness vacation, where the idea is to learn to curb those pound-building cravings.

Within a few hours' driving distance of Washington are a number of weight-loss programs, some informal and others quite serious. Most feature daily exercises, nutrition classes and specially prepared low-calorie meals.

The informal programs help you trim pounds and tone up muscles in a vacation setting -- at the beach or in a mountain resort. They run from a weekend to a week or more, are moderately priced, and mostly are for people whose primary goal is looking sleeker in a swim suit and staying that way.

The more serious programs are typically (though not necessarily) for people with more severe weight and health-associated problems. The city of Durham, N.C., home of Duke University Medical Center, has become a center for diet control for those whose weight reduction requires medical supervision. There are at least four such diet programs, and while they really aren't vacations (except as a change of pace from a normal work week), you do have the support of others in a group.

Stays in Durham generally range from a minimum of one week up to two months or more. You should consult your physician before choosing a program. The price, because of medical tests and supervision, is much higher than at the informal programs. In some instances, at least part of the cost may be covered by health insurance.

Losing weight is not easy, but it can be easier in a weight-loss program, where you have supervision, instruction and the reassurances of a group of like-minded souls. You often find yourself not wanting to disappoint the rest of the bunch by dropping out.

Actually, much of what you do in these programs, especially the informal ones -- swimming, tennis, hiking -- is exactly what you would do on a regular holiday. Only you probably will go at it a bit more rigorously, and, more important, you won't spoil the effect afterwards with several beers and a bag of potato chips.

Weight-loss vacations are also part learning vacations, because typically you are instructed on low-calorie food preparation -- lessons that can help maintain any weight loss. Often husbands and wives, both feeling uncomfortably pudgy, take a diet vacation together. Sharing, it seems, eases many challenges.

Among the informal weight-loss programs for a week's vacation or a weekend getaway (for adults):

*Coolfont Re-Creation Center Berkeley Springs, W.Va.

Coolfont is a comfortable year-round resort in the scenic woods of eastern West Virginia. Depending on the season, it offers swimming, fishing and boating on a large lake; horseback riding; hiking on miles of trails; tennis; and ice-skating and cross-country skiing.

The resort has developed a variety of health-related programs that include five-day "health retreats" for the diet conscious; fitness weekends; weekend massage workshops for beginners and experienced practitioners; personal stress-management weekends; and a five-day "smoke-free" program.

The health retreats combine exercise, a low-calorie diet and diet instruction, as well as the pleasures of a hot tub and sauna -- nice rewards for sticking to the regimen.

A typical day begins with a 7:30 a.m. walk, followed by stretching exercises before breakfast. After breakfast, there may be a short discussion on enjoying a healthy life style. Then everybody puts into practice what he or she has learned by joining in a series of aerobic exercises.

The afternoon brings another walk, additional exercises and perhaps some more strenuous pursuit, such as tennis or (in winter) cross-country skiing. After-dinner activities include massage instruction, square dancing or a pop or classical concert in one of the lounges.

The five-day program begins at about $300 per person (double occupancy). Seven- and 12-day programs also are available. Accommodations are in individual hillside chalets or in the Woodland House Lodge.

For more information: Coolfont Re-Creation Inc., Berkeley Springs, W.Va. 25411; (304) 258-4500. Direct from Washington: 424-1232.

*The Woods Fitness Institute Hedgesville, W.Va.

You'll find saunas and whirlpool baths here for pampered relaxation, but the Woods Fitness Institute (formerly Eastern Fitness Institute) nevertheless advertises itself as a "no-nonsense" outfit. The institute is part of a new resort, The Woods, adjacent to 22,000 acres of state forest land and miles of hiking trails.

The resort's recreational facilities include indoor and outdoor swimming pools, tennis courts, muscle-building equipment, an athletic field, and a small pond for fishing in the summer and ice-skating in the winter. Accommodations are in modern cabins or an attractive motel-like lodge.

The minimum enrollment in the fitness program is for one week. The goal of the program is not only to lose weight but also to learn proper eating habits to keep the weight from returning. Participants are weighed and submerged in water to determine the percentage of body fat.

A typical day begins at 7:30 with two- to three-mile pre-breakfast walk. After breakfast comes a set of stretching exercises for flexibility, followed by lectures and films on diet, nutrition, exercise and human physiology.

Time out for lunch, and then the afternoon is devoted to "play" activities: hiking, volleyball, tennis, racquetball, canoeing and softball. Participants are encouraged to join in all the activities, but they don't have to.

A one-week program begins at about $550 per person (double occupancy). A full month is about $1,750 per person.

For more information: The Woods Fitness Institute, The Woods Resort, P.O. Box 5, Hedgesville, W.Va. 25427; (304) 754-7977.

*Slender Shore Bethany Beach, Del.

Slender Shore, a program for women, is offered several weeks a year in spring and summer. Lodging is in the Sea Colony apartments on the Atlantic shore in Bethany Beach, and facilities include an indoor swimming pool, tennis courts, health club and sauna.

The program is a combination of gourmet diet meals and individually designed exercises, yoga and recreational activities. Participants jog and hike on the beach, ride bicycles, play tennis and swim.

It's part work, part group fun and part pampering, since someone else is preparing the meals. A week is about $590 per person (double occupancy).

For more information: Slender Shore, c/o 4119 Leland St., Chevy Chase, Md. 20015; (301) 652-6971.

*Weight Watchers Adult Camp East Stroudsburg, Pa.

The Weight Watchers program takes place on the Pocono Mountains campus of East Stroudsburg State College during summer break. The college specializes in physical education, so the athletic facilities are excellent: a large indoor pool, a track for jogging, tennis courts, baseball diamonds and a gymnasium with weight-lifting equipment.

The program is offered annually for eight weeks from late June to late August. Participants may sign up for one week or as many as they feel they need. Accommodations are in student dormitories, where couples can share a room. The specially prepared meals are served buffet-style in a private dining room. A one-week stay is about $495 per person; a month, about $1,790.

Most days include energetic "slimnastics" in the gym or in the swimming pool followed by tennis, swimming lessons and other sports. Afternoons are somewhat less strenuous. This is a time devoted to health lectures, such as how to order a diet-conscious meal from a standard restaurant menu and not feel deprived, and low-calorie cooking classes.

For more information: Weight Watchers Adult Camp, 183 Madison Ave., New York, N.Y. 10016; 800-223-5600.

Among the medically oriented weight-loss and diet-modification programs, all located in Durham, N.C.:

*Structure House

"Within an atmosphere of acceptance and understanding," promises Structure House, "people lose weight, develop positive feelings about themselves and learn how to make the changes in life style and behavior that are necessary to long-term weight control."

Three meals a day, totaling 700 calories, are served in the Structure House dining room. Counseling, diet classes, swimming and hiking are part of the day's schedule. Participants stay in apartments located 1 1/2 miles from Structure House. A month's enrollment is $2,475, which includes initial diagnostic evaluations, meals and lodging.

For more information: Structure House, 707 Morehead Ave., Durham, N.C. 27707; (919) 688-7379.

*Duke University Diet and Fitness Center

Plan to stay for at least a month -- two, if possible -- advises the Duke University Diet and Fitness Center. The program includes medical and fitness evaluations; exercises in a large gym and indoor pool; and lectures promoting healthier eating habits.

The cost is about $2,000 for the first month and $1,240 for a second month, not including the cost of laboratory studies or lodging. Accommodations can be arranged in hotels, motels and rental apartments in the vicinity of the fitness center.

For more information: Duke University Diet and Fitness Center, 804 W. Trinity Ave., Durham, N.C. 27701; (919) 684-6331.

*Kempner Clinic "Rice Diet"

This specialized low-calorie, low-fat and low-salt diet program is directed mostly at seriously overweight individuals who, as the Kempner Clinic requests, are "prepared to stay with us without any interruption until you have reached a normal weight level." This may take from weeks to months.

An initial medical evaluation is $1,100; daily consultations and testing are $165 a week; and meals are $63 a week. Accommodations are not included but can be arranged.

For more information: Kempner Clinic, Box 3099, Duke University Medical Center, Durham, N.C. 27710; (919) 684-3418.

Stuelke Institute "Thin for Life" Clinic

*The Stuelke Institute program is a four-week, 700-calorie-a-day plan that combines diet with patient education and counseling and exercise, principally walking. It is open to anyone with a weight problem due to overeating, from individuals wanting to drop only a few pounds to those who must lose massive amounts for serious health reasons.

The basic price for the initial 28 days is $2,086, which includes all meals, medical examinations, group therapy and classes. Each additional week is $259. Basic hotel accommodations nearby begin at $140 to $160 a week.

For more information: Stuelke Institute, P.O. Box 2894, Durham, N.C. 27705; (919) 683-5547.