HOUSTON (AP) _ Oil-eating bacteria worked when sprayed on a sensitive marsh fouled by a July oil spill, proponents say, but some scientists say they're still worried about the safety of the cleanup technique.

Speaking at a symposium on bioremediation at Lamar University in Beaumont, proponents of the technique reported that microbe-treated areas of Morrow Marsh, on Galveston Bay, were largely free of oil a month after the spill.

Franz Hiebert, director of geoscience programs for Alpha Environmental Inc., said researchers ''found a wide variety of fishes swimming in and out of the marsh'' in the northern reaches of the bay near Cedar Bayou.

Hiebert's company sprayed the oil-eating bacteria in the marsh and other areas of Galveston Bay fouled by 700,000 gallons of oil that spilled when a tanker collided with oil barges in the Houston Ship Channel.

The bacteria also were used in June, after the supertanker Mega Borg exploded 57 miles off Galveston.

Not everyone at Tuesday's conference rallied behind bioremediation, which has been used for years to treat sewage and hazardous waste and only recently was used on oil spills.

Although studies done so far have been ''very encouraging,'' there ''is plenty of research yet to be done,'' said Sarah Liehr of the Department of Civil and Environmental Engineering at the University of Houston.

Among the issues to be resolved is whether phosphorus, nitrogen and other nutrients mixed with the bacteria to stimulate their growth will cause algae to bloom or reproduce explosively. Algae blooms can deplete oxygen in the water.

Norm Novick, of Mobil Oil Corp.'s Toxicology Department, said the process clearly works on contaminated soils, sludges and groundwater. He said it has limited usefulness in cleaning up heavier petroleum products.

Novick maintained that in most oil spills ''the organisms you need (to eat the oil) are already there.'' Evidence suggests that indigenous bacteria only need stimulation by nutrients to degrade spilled oil and that additional bacteria aren't needed, he said.

Texas Water Commission Chairman Buck Wynne III said that during two recent spills ''the one thing we did show was that (bioremediation) didn't hurt anything.''

It cost the state about $90,000 to treat the June and July spills, he said.

Wynne expressed doubts that bacteria will be used routinely on spills until the technology wins the support of the federal government.