A new microbe that eats nothing but toxic chemicals has been created in an Illinois laboratory, opening the way to new methods of cleaning up chemical spills and scouring the 10,000 dangerous toxic waste dumps around the country.

"We hope to make toxic chemicals biodegradable," said Dr. A. M. Chakrabarty, of the University of Illinois at Chicago. The method used to create the bug should have the capacity to create not one, but an army of such microbes to eat different toxic chemicals, he said.

"During the past several decades the release of various synthetic chemicals . . . into the environment has resulted in serious environmental pollution. The problem is not only the toxicity of the chemicals, but their persistence, so that they ultimately contaminate human bodies," wrote Chakrabarty in a report in the Dec. 4 issue of the journal Science.

An example is a hazardous plant-killing chemical called 2,4,5-T, which is suspected of causing birth defects.

Combining old breeding techniques with new genetic methods, Chakrabarty and his colleagues S. T. Kellogg and D. K. Chatterjee, have created a new bacterium which until now has not existed. It lives solely on a diet of 2,4,5-T and a few other related chemicals.

At the relatively high concentration of 1,000 parts per million of 2,4,5-T in the soil, the new bug will eat more than 98 percent of the chemical in laboratory conditions, Dr. Chakrabarty said.

Chakrabarty expects to unleash the bacteria in field tests this spring, probably in areas such as those highly contaminated by the U.S. Air Force target-practice with Agent Orange. The concentrations in those areas are as high as 20,000 parts per million, or about two percent of the soil content. It has remained at high levels in the soil more than 15 years because 2,4,5-T is degraded only very slowly in the environment.

"We can decontaminate the soil by applying the bugs once a week for six weeks," predicted Chakrabarty.

Chakrabarty, who is best known for his work on oil-eating microbes and his part in a landmark Supreme Court case in which the court approved his getting a patent for making a new life form, began this work by taking samples of microbes from such waste dumps as Love Canal, in New York, Eglin Air Force Base in Florida, and an Arkansas dump.

The microorganisms in the dumps over the years have become resistant to the chemicals.

Chakrabarty then inserted plasmids, little circles of DNA, into bacteria of the variety called Pseudomonas. On the plasmids were genes that produce an enzyme capable of degrading, or breaking up, the molecules of some toxic chemicals.

He placed the mixture of microorganisms and plasmids in a laboratory tank, with food in the form of different chemicals including 2,4,5-T. Gradually he increased the amount of 2,4,5-T in the tank. He hoped that over time, evolution on a miniature scale would occur, and the microbes would adapt to their environment by learning to eat more and more 2,4,5-T using their new plasmids.

It worked; eventually he had the bugs eating 2,4,5-T as their chief food.

Chakrabarty said that if his bugs come into common use to break up toxic chemicals, it might create an interesting reversal. "If you use 2,4,5-T to kill weeds one year, and then apply these microorganisms to clean it up, the microorganisms will clean up the 2,4,5-T and then their numbers will die out drastically when their is no more of the chemical to eat.

"But they would not necessarily die out completely. So the next year when you want to spray again, the few microorganisms left" would experience an enormous population boom as they devoured 2,4,5-T, and multiplied rapidly. This would make the spraying less effective.

The ground where the organisms had been laid down would be able to fight back when the chemical was sprayed. "You might have to use more of the chemical to kill the weeds. The chemical companies might sell more of the chemical. But it could now be degraded," said Chakrabarty.