A vaccine to knock out the most widespread human ailment next to the common cold -- tooth decay -- has been created and successfully tested in four U.S. labs. Decay and decay-causing bacteria have been cut by 50 to 80 percent in test animals and a few human volunteers.

Now the four research teams, in different parts of the country, are racing one another to produce a variety of the vaccine that will be effective and safe for human use. One researcher said a vaccine will probably be ready by the end of the decade, and possibly sooner.

The advent of the vaccine will "remake the whole dental profession," according to Dr. Michael Cole, researcher at the National Institutes of Health. He said that there already is a shortage of work for dentists in some areas where flouride, a chemical that fortifies teeth against decay, is present in the water supply.

The pressure on families to combat decay by their own efforts -- through good nutrition, regular brushing and flossing, and regular visits to the dentist -- will be relieved somewhat by the existence of the vaccine. But researchers say that the vaccine will not be a cure-all; consuming much sugar and not cleaning the mouth will still cause decay even in the presence of a vaccine.

All four of the competing teams working on the new vaccine have the same basic idea: to stimulate natural antibodies in the saliva. These antibodies attack the bacteria that cause decay, called streptococcus mutans, and apparently prevent them from latching onto the teeth to grow destructive colonies.

In people with illnesses that prevent production of saliva, and thus of these antibodies, tooth decay is quick and ruinous. "The teeth deteriorate practically before your eyes," said Cole. "Every tooth surface if covered with decay within weeks."

The antibodies in the saliva defend against this disaster, but cannot succeed completely against the modern, sugar-laden diet.

To stimulate the body to make more antibodies, a vaccine is created, consisting of dead streptococcus germs or parts of them. These foreign bodies, when introduced into the body, stimulate a large increase in antibody production -- five-fold or more.

One vulnerability of streptococcus mutans is that it must have a way of attaching itself to the teeth before it can create decay. The bacterium apparently has an appendage that latches onto the protein coating on teeth -- the thin, transparent film called the pellicle.

The new vaccines, in the theory of how they work, get the body to make antibodies to block streptococcus from taking hold of the pellicle proteins. Homeless, the bacteria are harmless. They cannot build colonies, produce plaque (the yellowish material that dentists scrape off when cleaning teeth) or fill the plaque with destructive acid.

There are now two barriers to public availability of the vaccine. One is the problem of finding just the right antigen -- the right bit of dead bacteria that will evoke antibodies most effectively. The other is to be certain of the safety of the vaccine.

It was reported in one study that certain antibodies against streptococcus mutans also attacked heart muscle and caused serious heart problems in rabbits. This effect has not shown up in any of the other vaccine studies in rats, monkeys or humans, but it is possible that long-term use of the vaccine might eventually weaken the heart.

"We have the vaccine; it works, we know that. It is at the stage that some 60 years ago scientists would simply be giving it to people right now," said Jiri Mistecky of the University of Alabama. "It will be so many years before the public may get it because we are so much more cautious in these times. Pasteur knew nothing about how [his vaccines] worked. He simply did it. Now we must be sure."

An important side benefit is that the vaccine research will have implications for many other diseases besides dental decay. The immune system of the body probably works in a similar way in all the various exposed wet membranes -- such as eyes, lungs, and sex organs.

What is learned in studies of dental decay may be important in finding vaccines for choler, gonorrhea, salmonella, some varieties of pneumonia, infant diarrhea and other aliments.

One important finding in the past few years of research on caries (the disease of dental decay) is that the antibodies for all these mucus membranes are formed originially in the intestines. As these develop, they migrate out to the membranes and seed the organs that create mucus, saliva, tears, and the other fluids that protect the membranes.

The caries vaccine finally put to use by the public is likely to be an oral vaccine that operates by stimulating the center of anitbody production in the intestine first or in combination with some method of stimulating the production of antibodies directly in the glands that make saliva.

The four groups that have been working on the vaccine are at the NIH under William Bowen, at the University of Alabama under Jerry McGee and Jiri Mistecky, at the Forstyth Dental Center in Boston under Martin Taubman, and the State University of New York at Buffalo under Robert Genco and Richard Evans.

"This will be a great step forward," said Taubman of Forsyth, "and in a couple of generations there will be far less dental caries. But this will not wipe out caries altogether. You have to remember there are three important factors -- the diet, the bugs that cause caries and the resistance of the host to the bugs. The vaccine works only on the resistance of the host."

Anti-microbial agents to kill the streptococcus outright are also being tested now in several laboratories, and the American Dental Association is determined to get dentists to concentrate more and more on the third factor -- diet and cavity prevention.

John Coady, executive director of the association, said that there are enough problems in dentistry still to be solved so that the profession will survive if dentists begin to change the emphasis in their work from tooth grinding and filling. Care of the gums, preventive work and raching persons rarely treated before -- such as the retarded, the aged and the handicapped -- are the new priorities for the profession, Coady said.

Almost half the population, he said, gets either no treatment or very infrequent treatment from dentists.In addition, most of the tooth loss that occurs in people over the age of 20 is, caused not by decay but by gum disease, so dentist in the future may be concentrating their efforts on gums rather than teeth.

Still, most dental researchers concede that with fluoride, a new vaccine and other possible anti-decay drugs coming into use in 10 years, constantly growing numbers of dentists cannot be supported.

Over the past 10 years, the number of dentists jumped 21 percent, the population only 8 percent. At the same time, ADA statistics show that the patient load dentists are carrying has already begun to drop about five patients a week in recent years.