Bacteria discovered growing at the bottom of a lake in what once was the throat of a volcano are the strongest evidence yet that warm water is flowing into the lake, two researchers say.

That discovery by Jack Dymond and Bob Collier of Oregon State University puts them in the middle of a controversy involving proposed geothermal energy development near the 1,932-foot-deep Crater Lake, which is the main part of a national park.The National Park Service and some environmental groups are concerned that drilling for underground hot water or steam could affect the lake, formed when a volcano exploded and collapsed into itself.

Dymond and Collier announced Friday, after three weeks of exploring Crater Lake in a one-man submarine, that they had found evidence that hydrothermal vents, or hot springs, do exist on the lake floor.

"The main focus of that venting was around some large bacterial mats, an exotic lifeform that we don't believe exist in other parts of the lake," Dymond said at a news conference.

He said the mats were "clearly associated with warm waters that are coming up through the rocks."

Dymond said temperatures recorded at the mats were almost 11 degrees warmer than the surrounding water.

California Energy Co. is trying to tap the geothermal potential of the area, still warm from past volcanic activity, but legislation that would place Crater Lake National Park on a list of other national parks with "significant hydrothermal features" is now pending in Congress. Such a designation could halt drilling leases outside the park.

Determining if there is a link between the vent area and the site of the proposed geothermal energy plant in Winema National Forest some 41/2 miles away would be an "extremely difficult problem" even with the most modern scientific equipment, Dymond said.

But he emphasized that the bacterial mats are the best evidence yet of vents because the mats "are a lifeform that is not based on photosynthesis ... but is based on the chemicals and chemical energy that's available within the fluids that are coming up from within the rocks."

Collier described the bacterial mats, first found at a depth of about 1,500 feet, as "big clumps of cotton plastered over the face of a wall."

The potential impact of the research on geothermal development "would be pure speculation at this time," said Peter Thompson, chief ranger for the National Park Service at Crater Lake.

Joe LaFleur, a geologist with California Energy, said Friday that he still doesn't believe there is enough evidence to confirm the theory that heated ground water is entering the lake, primarily filled by rain and snowmelt.

Regardless, LaFleur said the company's proposed geothermal plan would not affect the lake or the park.

The research is part of a 10-year study of Crater Lake by the Park Service, which will end in 1992. This summer's research was funded by a $225,000 Park Service grant.