As many as 50 percent of the dogs brought into veterinary hospitals in the United States are obese.

Experts such as those at the Quaker Pet Nutrition Center and the American Animal Hospital Association point out that obesity is becoming an increasing problem for dogs - perhaps the "couch potato" syndrome is spilling over into the nation's pet population.A dog is considered obese if it weights at least 10 percent more than its ideal weight. Like obesity in humans, it is most likely caused by too many calories and not enough exercise. And like obesity in humans, it can lead to serious health problems such as high blood pressure, increased diabetes risk, lowered resistance to diseases, heart and respiratory complications - and a shortened life span.

Some breeds of dog are more prone to weight problems than others. Labrador retrievers, cocker spaniels, dachshunds and beagles tend to pick up weight faster than leaner breeds such as poodles, Irish wolfhounds, German shepherds and boxers.

It's easy to tell a grossly obese dog. But how can you tell if your dog is getting a little soft around the edges?

A normal, healthy dog has a clearly defined waistline, called a tuck-up, behind his rib cage. If your pet no longer has a tuck-up or if he has such fat protrusions as a sagging abdomen or swollen pockets of fat on the hips, he's carrying more weight than he should.

Run your hand along the animal's rib cage along the underside of his trunk. A dog of normal weight has a very thin layer of fat over-lying the bone structure. If you can't feel or see the outline of the ribs, it's probably time for a weight reduction program.

The first step should be a visit to the vet to set up a diet and exercise program.

If doggie needs a diet, gradually reduce his caloric intake by feeding him a little less each day or by putting him on a reduced-calorie diet specially formulated for obese dogs. You may want to give him two or three smaller meals each day. This will help satisfy his hunger, ease his digestion and keep him from scrounging from food. Your vet can tell you how much food your pet needs in order to lose weight safely.

Feed the dog only at designated mealtimes; many dogs eat normal-sized meals and then fill up and out on treats given by well-intentioned humans.

A dog that begs is often as hungry for attention as for food. He'll be healthier and thus happier if you give him a loving pat on the back rather than a tidbit from your plate.

Gentle, consistent exercise helps your dog lose weight as well. Walking is the simplest way to give your pet the exercise he needs. Try to schedule a couple of short walks a day, and watch closely for signs that your dog may be tiring - such as shortness of breath. Obese dogs, particularly old ones, tire more quickly than relatively fit dogs do. Vigorous activities like running, jumping and fetching may be too strenuous for the pets that are out of shape or elderly.

Walking up and down the stairs can be an effective exercise for an older dog. You can also make him exercise by following you around the house.

Remember, too, that overweight dogs are less tolerant of temperature extremes. In the summer they can easily become strained and suffer a heatstroke.