FOR VACCINES, the normal economics of the market does not work well. There is now only one supplier in this country for each of three crucial vaccines. The three are given to nearly every child and, among them, the three protect those children against seven dangerous and highly contagious diseases. Public health authorities have been concerned for some time about the wisdom of relying on sole sources for products of such incalculable importance.

The current shortage of DPT vaccine will probably be neither severe nor prolonged. Sufficient vaccine actually exists to meet the need, but one manufacturer, Connaught Laboratories, has taken its product off the market because it cannot get adequate insurance against product liability suits. DPT means diphtheria, pertussis and tetanus. The pertussis, or whooping cough, component can cause damaging and even fatal reactions in some children. There were three suppliers last spring, but, because of fears of litigation and trouble over insurance, two have dropped out of the market.

That leaves one, Lederle Laboratories. It is also the only supplier of the oral polio vaccine. Similarly, there is only one supplier, Merck, of the vaccine for measles, mumps and rubella. Last year the government began, on a modest scale, to stockpile these vaccines. The funds now available for that purpose -- about $3.5 million -- are one-tenth the cost of bringing the stockpiles up to the six months' supply of all three vaccines that the Centers for Disease Control consider desirable. Amid all the budget cutting of the year ahead, you might want to keep an eye on that small but essential item.

But stockpiling, while necessary, isn't sufficient. Dr. Martin H. Smith, speaking for the American Academy of Pediatrics, made that point at last week's hearing before Rep. Henry Waxman's House health subcommittee. Dr. Smith asked what might happen if any of the sole suppliers should cease production.

The drug companies want a public system of compensation for the victims of severe reactions to these vaccines. But Congress will have to do more than that. It is not the proper purpose of public policy merely to create comfortable monopolies, shielded both from damage suits and from competition. Some measure of protection from damage verdicts probably will be necessary. But to ensure adequate supplies, Congress will need to find ways to bring more producers into the field. Particularly in the case of whooping cough, it will need to generate competitive pressures for a better and safer vaccine. In recent years, the trend has only been toward less competition.