In the first attempt to control an oil spill at sea with oil-eating microbes, an entrepreneurial scientist yesterday sprayed 100 pounds of bacteria onto the slick generated by the supertanker Mega Borg, which is still leaking light crude off the Texas coast.

The experiment, endorsed by enthusiastic Texas officials, represents a potentially powerful new weapon for combating spills before they reach beaches and inshore bays and estuaries, where oil often does its greatest environmental damage to fish hatcheries and birds.

"If it works in the sea like it works in the laboratory, we're going to solve the problem of oil spills in this country," said Texas Land Commissioner Garry Mauro, who has taken interest in promoting use of microbes.

The concept, however, is receiving mixed reviews in the scientific community.

"I think snake oil would work as well as bacteria," said Richard Scalan, a research scientist at the University of Texas Marine Science Center in Port Aransas. "A lot of politics are involved in this whole thing."

While researchers have known for years that bacteria are capable of eating oil, many are skeptical that the technique can be used on large spills, which must be consumed quickly before they reach shore.

The scientists fear additional bacteria may serve only to break down oil into more toxic byproducts.

They add that special strains of bacteria may not be necessary, since similar microbes are present in the oceans and are limited only by available nutrients, such as nitrogen and phosphorus.

But proponents of the scheme believe the organisms will break down enormous quantities of oil, turning hydrocarbons into more benign byproducts.

They say the microbes will reduce the oil to an emulsion of fatty acids, which will sink and be consumed by marine life. The microbes will die when they run out of oil to eat.

A research ship operated by Texas A&M University was steaming toward the area where the bacteria were sprayed and is to collect water samples to gauge success of the experiment. Results are expected as early as today.

"Biological activity is all related to numbers. It's like building the Great Wall of China. It would take one coolie a million years to build or a million coolies one year to build. It's the same thing with bacteria," said Carl Oppenheimer, an oceanographer and microbiologist at the University of Texas and founder of Alpha Environmental, the Texas-based biotechnology company that was employed to seed the oil spill with microbes yesterday.

A similar technique to encourage microbes, employed on the beaches of Prince William Sound in Alaska after the Exxon Valdez spill, produced results that government scientists have called "spectacular," as beaches fouled by oil were cleaned up by resident bacteria that were encouraged to grow by addition of fertilizer. No foreign bacteria were applied.

Oppenheimer maintains that his bacteria are the most aggressive oil-eaters in the world. Collected from dozens of oily locales, including Boston Harbor, the microbes were bred in the laboratory and mixed and matched in vats to create "special blends" of superactive bacteria. All the microbes occur naturally and were not manipulated by genetic engineering.

The creatures, selected by Oppenheimer for their appetites and concentrated in a dry powder, were sprayed into the Gulf of Mexico yesterday about 60 miles off the coast of Galveston, where the Mega Borg's engine room fire was reported extinguished. The fire had hampered efforts to empty leaking cargo tanks and stem flow of oil into the sea, where the Coast Guard said 4.3 million gallons of oil had spilled, making it the nation's fifth largest tanker spill.

The Coast Guard earlier had estimated that the tanker had spilled 3 million gallons of crude, and it did not explain how it arrived at the higher figure yesterday.

Only about 22,000 gallons, however, remained in the ocean; the rest burned, evaporated or was skimmed, officials said.

The bacteria were applied only to a small section of the 30-mile spill, which could deposit tar balls on Galveston beaches today.

Some researchers, however, remain skeptical that Oppenheimer's "special blend" of microbes, reared under conditions that Oppenheimer would not reveal, will be capable of controlling a large oil spill. "The concept is controversial," said Mahlon Kennicutt, an associate research scientist of the Geochemical and Environmental Group at Texas A&M University, a leading institute for the study of oil in the sea. Kennicutt said bacteria long have been used to clean up sludge produced in oil operations.

"But the problem I have is that the area you're talking about is quite large. A spill can be tens or hundreds of miles. How do you seed an area that large?" Kennicutt asked. He and other researchers added that while the bacteria may break down the complex hydrocarbons contained in oil, it could leave behind quinones and napthalenes, which could be more toxic to marine life by penetrating cell membranes. Oil, on the other hand, merely coats the animals.

Researchers at the University of Texas Marine Science Center also were critical of the Texas General Land Office, which issued a report this week on tests at the center last year of Oppenheimer's bacteria with the marine science center's name emblazoned on the cover.

"It was a poorly designed study that we wanted no part of," said Patrick Parker of the marine science center, which allowed two of its large aquariums to be used for experiments last year.