Preliminary results from a nationwide survey show unexpectedly high acid levels in many Florida lakes but fewer acidified lakes in the Northeast than some scientists had predicted, the Environmental Protection Agency said yesterday.

But EPA officials cautioned that the results cannot be used to gauge the impact of acid rain or to predict which lakes may become acidified.

"This survey tells us how many lakes are acidic now, from whatever cause, but it doesn't say what that cause is," said Charles L. Elkins, head of the agency's air division. "It really does not give us all the answers we need, but it is an essential first step."

The survey, part of a multimillion-dollar research project into the causes and effects of acid rain, involved more than 1,600 lakes in the Northeast, upper Midwest, Florida and the southern Blue Ridge Mountains.

According to the survey, one in five Florida lakes have pH levels of less than 5.5, which is moderately acidic; and one in eight lakes there show highly acidic readings of less than 5.0. A pH reading of 5.0 is five times more acidic than a reading of 5.5.

In the Northeast, fewer than one in 10 lakes were found to be moderately acidic and about 4 percent, or one in 25, fell into the highly acidic range.

In the upper Midwest, 4 percent of lakes were moderately acidic and 2 percent highly acidic. The survey found no lakes with pH levels at or below 5.5 in the southern Blue Ridge, which included parts of North and South Carolina, Tennessee, Georgia and Virginia.

Acid rain, which has been blamed for damaging aquatic life and forests, is believed to be linked to sulfur emissions from coal-fired power plants and factories. In the past, most concern over its effect has centered on the northeastern United States and Canada, where prevailing winds carry pollutants from the heavily industrialized Midwest.

Elkins said the survey results should be somewhat reassuring to residents of the Northeast "to the extent that they have been led to believe that thousands of their lakes are acidic."

But he added that the EPA did not expect to find such high acidity in Florida.

"From these data alone, you can't conclude Florida has an acid rain problem," he said, but he suggested that residents "now should be more concerned about their water than they have been."

Richard Linthurst, who directed the survey, said many of Florida's lakes may be naturally acidic because of runoff from pine forests and heavy vegetation. Relatively high levels of such organic acids do not necessarily spell trouble for aquatic life, he said.

But he added that not all of Florida's acid lakes can be attributed to natural causes.

The study met with skepticism from some environmentalists.

"I don't think it says very much," said Steve Howards of the National Wildlife Federation. "We're teetering on the brink of a crisis, and they're telling us we haven't gone over the edge. We don't find that very reassuring."

"The issue has always been the trends," Howards said. "The question is how short do we want to let the fuse burn?"

EPA officials acknowledged that their initial lake survey is not very helpful in assessing trends. Courtney Riordan, head of the acid rain research office, said the agency hopes to make some predictions when additional research is completed within the next two years. The agency is conducting similar lake surveys in the West, but preliminary results are not available.

The survey also measured the lakes' ability to neutralize acid. By that measure, about 60 percent of the Northeast's lakes and 54 percent of Florida's lakes were considered "potentially vulnerable to acidification."

In the upper Midwest, 41 percent of lakes were potentially vulnerable; in the southern Blue Ridge, the figure was 36 percent.

But EPA officials said those figures also were of "limited use", because the one-time test did not indicate whether a lake's neutralizing capacity was decreasing or holding steady.