TRAVELERS, especially those heading for Latin America, Southern Europe, Asia, and Africa, have long been accustomed to getting admonitions like these:

Don't drink the water.

Don't eat uncooked vegetables.

Avoid ice cream, whipped cream and other products that may have been made from unpasteurized milk.

Now a new and perhaps far more important warning should be added:

Beware the physician who prescribes drugs, and also the pharmacist who may both prescribe and dispense them, who may be unaware of the limited value of these products and of their potentially harmful or fatal side-effects.

Last year, after a long, in-depth study in Mexico, Central America and South America, it was disclosed that some of these health professionals are giving out a potentially deadly antibiotic to patients suffering from such trivial infections as tonsillitis and laryngitis.

Some have treated depression with a combination of drugs that can interact to cause death.

Some are keeping patients on steroid hormones for such prolonged periods that some have suffered from bone-softening, pressure fractures of the vertebrate, psychotic changes and flare-ups - sometimes fatal - of latent tuberculosis and other infections.

Some have administered excessive dosages of potent anti-arthritis drugs, resulting in serious or lethal damage to the blood-forming tissues.

These and similar prescribing blunders, now thoroughly documented by Latin American hematologists, pathologists and other experts, do not mean that Latin American physicians and pharmacists are poorly trained, poorly motivated or unable or unwilling to keep up-to-date. Some of the health care rendered in the Latin American countries is fully comparable to the best medicine practiced in Washington, Boston, London or Stockholm. On the other hand, some medical care rendered in Latin America is as poor as the worst practiced in the United States.

instead, this misuse of drugs in Latin America - and also in such other countries as Spain, Egypt, India and Taiwan - appears to be a reflection of the astounding drug promotion and drug labeling disseminated to physicians and pharmacists by much of the pharmaceutical industry. In this "educational" material furnished by many drug companies, the efficacy or usefulness of the drugs is too often gorssly exaggerated, and the possible hazards are minimized, glossed over or totally omitted.

Or, the promotion may essentially warn the physician, "This drug may produce nose stuffiness," while failing to mention, "This drug may kill your patient."

In our investigation we compared the promotional material furnished to physicians in the United States and Latin America on 26 well-known, widely used prescription drug products marketed under 40 different brand names by 23 global pharmaceutical firms. Some of these companies were based in the United States. Others had their headquarters in Switzerland, France or West Germany.

In the United States, where drug promotion and labeling is under the strict control of the U.S. Food and Drug Administration (FDA), each company is required to limit its claims of usefulness to those that can be supported by substantial scientific evidence. All potential hazards must be clearly disclosed, and occasionally FDA requires the warnings to be printed in extra large type.

In the Latin American countries, however, a different situation prevails, and the companies generally say whatever they want to say.

One of the most notable cases has involved the antibiotic chloramphenicol, marketed in many countries by many different companies.

In the United States, it is described as indicated only for such life-threatening infections as typhoid fever, Rocky Mountain spotted fever, a rare form of meningitis in children and a few other conditions in which it is considered clearly the drug of choice. Physicians in this country are warned that it may cause infrequent but serious side-effects, including a blood disorder known as aplastic anemia that, in some cases, carries a mortality rate of 30 to 60 per cent. The drug, the labels say, should not be used for trivial infections.

But in Latin America, some companies have recommended chloramphenicol for laryngitis, tracheobronchitis, pneumonia, gonorrhea, syphilis, abscesses and other diseases in which other and safer drugs can be used. In those countries, thewarnings and contraindications are minimal or entirely omitted.

When this situation was called to the attention of the drug companies concerned, the responses included such explanations as these:

"Latin American doctors don't need any warnings. They already are aware of the dangers" - an explanation that infuriates medical educators and other experts.

"Things are different in Latin America" - a view that seems to suggest that drugs are fare more effective and safer south of the Rio Grands.

"What's involved her is an honest difference of opinion - we feel we have enough evidence to show that our drug is acceptably safe, but we can't convince the Food and Drug Administration."

This last explanation would probably be more palatable if the company said one thing in the United States, where its statements are under the heavy hand of FDA, and something different in all of Latin America, where the rules are less rigid.

"But," said one Colombian health official, "when we find the company tells one story here in Bogula, another in Quito, anothe rin Braslia and still another in Mexico City, that is difficult to comprehend."

Finally, drug companies have put up as their major defense, "We're not breaking any laws." They claim that their foreign subsidiaries of affiliates are managed by nationals of the country who know the laws and regulations, and who obey them scrupulously.

Our survey, including an examination of Latin American drug laws, showed that this defense was valid in some countries. The companies were not violating any drug promotion laws because no such laws were in existence. In others, the situation was unclear, with the laws difficult to analyze. But in at least four countries - Colombia, Honduras, El Salvador and Panama - laws controlling drug promotion are on the books, and companies were breaking those laws.

So far as we can determine, none of these practices can be controlled by U.S. laws.

Complicating the situation are other factors:

Most Latin American physicians are employed by the government and paid relatively low salaries. In contrast, the company detail men - the "visitadores" who promote their products to physicians - are employees of private industry, usually paid at least party by commissions, and not inclined to knock their own drugs. Many of these detail men have had only a high school education.

Although many drugs legally require a prescription written by a physician, this requirement - except for morphine and its relatives, and for some tranquilizers - is frequently ignored. In most pharmacies, a patient can get a prescription product merely by asking for it. Or the patient can describe his symptoms to the pharmacist, and the pharmacist will then diagnose, prescribe and dispense.

If a patient is injured by a prescription drug, the company, the physician and the pharmacist are generally safe from retribution. There are essentially no effective medicalmalpracticeor product liability laws in most of the countries.

As an example of what can happen in this complex situation, we observed the case of a woman - thin, nervous, jittery - who went into a large pharmacy in Costa Rica and asked by name for the potent tranquilizer. The clerk said he had something far better, and sold her a supply of what we recognized as a powerful but dangerous thyroid drug. It may have been the appropriate drug for her. But what made the event memorable is that we were unable to tell whether the clerk - who acted without consulting any of his colleagues - was aged 14, 13 or 12.

Since these findings were published in May of 1976, and simultaneously presented in testimony before the U.S. Senate Subcommittee on Monopoly, there have been signs that the situation may be corrected more swiftly than had been anticipated:

The findings were widely reported throughout Latin America by newspapers, radio and television.

In a number of global drug companies, some officials - especially those concerned with research and medical affairs - are urging their firms to follow the same promotional policies they use in the United States in all their foreign promotion.

The United States delegation to the International Federation of Pharmaceutical Manufacturers has called for standardized drug promotion, worldwide, with full disclosure of hazards.

At least one major drug company in this country has already changed its promotion in Central America, limiting the claims for its products and disclosing their dangers.

Until all companies follow this lead, however, many physicians and pharmacists in many countries may continue to be uniformed or misinformed, and travelers should remain forewarned.