DOCTORS from 25 nations warned this week that the "flagrant misuse" of antibiotics has caused a "worldwide public health problem." Their statement will come as a surprise to many Americans -- including most doctors. The evidence documenting the rapid rise of bacterial strains resistant to these drugs is not yet widely known or appreciated. But it is compelling.

The phenomenon itself is nothing knew. When a population of billions of bacteria in a single person is attacked with an antibiotic, most will be killed. But if there has been a mutation in just one of them that renders it resistant to the drug, that one cell will flourish. If the antibiotic stays around for some time, that cell's descendants will eventually dominate the population. It is a classic demonstration of natural selection.

What is new is the unexpected rapidity with which genes that confer resistance are spreading throughout the world. Just a decade ago, doctors throughout the world. Just a decade ago, doctors could treat urinary tract infections with ampicillin -- a particularly effective drug against such problems -- with high confidence that the infection would be cured. Today, 20 percent or more of urinary infections are resistant to it. Gonorrhea is another disease that has developed a high level of resistance, in this case to penicillin.

The cause of the problem is the worldwide overuse of antibiotics. In some countries, especially developing nations, they are available without a prescription. In the United States, they are widely overprescribed. Both doctors and patients are responsible for that. Antibiotics are often given for too long or in too large a dose to sick patients who need them. Few doctors haven't met the patient who is disappointed if he leaves an expensive office visit with a prescription -- even if the problem is a cold and even though the doctor knows that colds are caused by a virus and are therefore not susceptible to antibiotic treatment.

Another serious problem in this country is the use of antibiotics in livestock feed to prevent disease in overcrowded feedlots and to promote growth. The evidence linking this practice to drug resistance in humans is suggestive but still controversial. There is no need to wait for final proof. The United States should promplty adopt the European compromise of limiting such use to antibiotics that are not used in humans.

If present trends continue, the day may not be far distant when doctors are faced with human infections resistant to most available antibiotics. Nor is there an unlimited supply of safe and affordable new antibiotics. There is a need for everyone -- doctor and patient, developed and developing nation -- to understand that the "wonder drugs" that have transformed mankind's health are themselves in serious danger.