LIKE MOST housepets everywhere, one New York City dog eats pretty much the same thing every day. But what is familiar food to him may surprise most other dogs and their owners.

Breakfast is cottage cheese, orange sections, wheatgerm, whole-wheat bread. Dinner is chicken, rice and/or potatoes, fresh vegetables, oil, an occasional egg yolk, more wheatgerm. Bed-time snacks are yogurt or cottage cheese, wheatgerm, perhaps a piece of fruit. A multi-vitamin and mineral supplement and extra vitamin E are added to the main meal; vitamin C is added to all.

The menu and three daily feedings derive not from an urge to spoil the pet, but from compliance with veterinary medical advice. The dog in question -- a 10-year-old German short-haired pointer with a history of gastrointestinal upsets -- was found to respond best to a diet not only free of preservatives, additives and commercial pet foods, but also heavy in fresh produce and dairy products. Of the diet staples, only the chicken -- a canned non-commercial pet food prescribed by the veterinarian -- and the multi-vitamin are dog foods per se.

Diet change may not solve every canine health problem nor can it necessarily obviate medical treatment. But in the case described above, after two years on the modifed diet, the dog remains free of the symptoms that hounded him for so long. This dog's return to good health and vitality was the result of what veterinarians term the conerstone of their tretment: nutritional guidance and diet planning.

The veterinarian responsible for the pointer's success story is Dr. John W. Higgins, on the executive board of the Veterinary Medical Association of New York City and direcor of the Yorkville Animal Hospital, who said pet owners "commonly" ask about nutrition, citing what he calls "a very obvious correlation" between interest in human health and that of pets. "I think the influence of diet is quite important," Dr. Higgins stated, an opinion he has reached after years investigating animal nutrition in depth as a personal research project.

In the opinion of another New York veterinarian, Dr. Irving Stern, "The most significant factor in a dog's health is diet." Other veterinarians concur; proper diet is basic to good health and the ability to recover from illness and injury. What a dog eats -- and how often -- must be judged against his physical condition, age, activity, and specific health problems.

Dr. Higgins said he usually runs out of time, so eager are people for nutritional advice. "I say, 'Let's try something, see how we do.' You have to have an eternal balance for the conditions involved. So it's a juggling game. What was good at one time will not necessarily be good six months or a year later, especially in the development or state of disease."

By and large, dogs today eat comercial pet foods -- canned, semi-moist, dry.

The consensus among veterinarians is that commercial pet food generally provides the average dog with an adequate diet and good nutrition, but opinions vary as to how "average" any one dog is. Dogs are nutritional individuals, prone to food allergies, chronic digestive disorders, the degenerative troubles of old age.

Dr. Higgins explaines how he defines a dog's physical problem an alleviates them through diet modification. "It's a veterinary medical detective's job when you start to examine the causes of a disease. If it's of nutritional influence, correct that first. Otherwise you're going to have dire consequences."

Food allergies commonly cause kidney, liver, gastro-intestinal, and skin conditions. Of these Dr. Higgins said, "Why should a dog come in repeatedly for, say, diarrhrea? I want to find out why, not just cure the one incident. Nutrition, diet can do it." He recommends yogurt, which he has seen aid in treatment of gastro-intestinal problems; eggs; cottage cheese; hard cheese; some fruits; and vegetables, especially those heavy in cellulose -- string beans, carrots, celery, lettuce. "I think dogs like the crunchiness of them," he added.

Dr. Stern, who believes "all commercial foods need supplementation," ranks eggs and cheeses at the top of his must-eat list, followed by unprocessed, wholegrain breads, fruits and vegetables.

Dr. Richard E. W. Vargoshe, who with Peter Steinberg is author of "The Household Book of Animal Medicine" due out later this year from Prentice Hall, recommends eggs, dairy products, and, for fiber content and nutrition, especially when dogs are finicky eaters and eschew. commercial foods, vegetables.

Stressing that dogs must be "not well fed but fed well," Dr. Higginsd said, "I think you can relate longevity to diet or shall we say, lapses in diet or bad feeling patterns." Dogs do best on a consistent approach toward feeling as toward obedience.

Dr. Robert Cohen of the Animal Medical Center explained that bad feeding habits stem from misconceptions of a dog's needs. "It's the old Jewish mother concept where we want to give our children -- in this case, our animals -- more than we had for ourselves. Unfortunately, dogs are not children." Dr. Cohen estimated that, as a result, "some 50 percent of our time is spent in treating human neuroses and not canine physical problems."

How often should dogs eat? Dr. Vargoshe, who pratices on Manhattan's West Side, said, "It's my personal opinion that they do better on two meals," citing the closeness many dogs feel toward their families and the distress they suffer when excluded from the social experience of eating together. "I think the animals are happier," said Dr. Vargoshe, "and many times the people are too." Dr. Stern's view is that dogs should eat at least twice a day, a practice Dr. Higgins seconds, especially for older dogs. Dr. Cohen generally suggests one daily meal for adult dogs free of gastro-intestinal or other diet-related symptoms.

Dr. Stern warns against over-reliance on any one pet food -- "People think a food is good per se and use it exclusively" -- and is vehemently opposed to feeding nothing but dry dog food, particularly to the larger breeds who face a potentially life-threatening condition (acute gastric torsion) directly related to feeding.

Most veterinarians cite overfeeding as the most common mistake owners make. Dr. Vargoshe believes "many pets are over-weight because of the emotional attitude of the owner, rathern than because the pet is hungry." Begging, encouraged unintentionally or simply tolerated, can result in "sort of an emotional appetite" on the dog's part, Dr. Vargoshen reasoned.

Veterinarians recognize a human problem behind obesity in dogs and admit little success in slimming down a dog whose owner remains overweight. Among the hazards of obesity listed by Dr. Higgins are skeletal breakdown, serious organ disorders, and shortened life-span.

How essential vitamin supplementation is in the adult dog is a question on which veterinary opinion differs. An adequate diet may supply enough: however, ascertaining the adequacy of an individual dog's needs and discovering any malabsorption problems can be difficult. Of regularly adding extra canine vitamins, Dr. Vargoshe said, "It certainly doesn't do them any harm. It's probably wise to use (vitamins) all their lives." Dr. Stern's opinion is that only a diet including fresh foods meets vitamin demands.

Dr. Higgins, who routinely advises using supplements, is a vitamin C advocate. Ascorbic acid, which, he explained, is manufacturd in the dog's body "to a greater or lesser degree," can work well against many ailments, including urinary disease. Dr Higgins has used mega doses to good effect and prescribes vitamin C often, surmising that some dogs either do not manufacture enough or are unable to make use of what is produced internally.

Rare is the dog owner who hasn't succumbed to the irresistible urge to give the pet edible rewards. While veterinarians warn against excessive feeding of commercial treats, they acknowledge the human need to give and the canine need to please and perform. Dr. Stern suggests replacing biscuits and canine junk foods with bits of cheese, wholesome bread, celery, or apples because treats are " . . . part of the social relationship between the owner and the pet. They're essential."

Dr Higgins said, "If you have an absolute need to have oral gratification as far as your dog is concerned, why not take the intelligent approach?" His preferences: brewer's yeast, vitamin tablets, chunks of semi-moist dog food. Biscuits, he said, are "a way of administering to what you think are the dog's needs, to keep him satisfied." Bones are no better; Dr. Higgins called them "foreign bodies" unsuitable for feeding.

By supplementing with any number of foods they eat -- from vitamins to vegetables -- owners may help their dogs avoid or overcome a host of ills, from occasional constipation to serious allergic reactions. Said Dr. Cohen, "There's nothing wrong with human foods for dogs as long as it is well balanced, but most lay people don't understand what makes up a well-balanced diet for dogs." Therefore, owners should seek veterinary advice before making changes. Veterinarians will welcome the interest. "I'd concluded, "because I know then (the result) is going to be consistent."