BALTIMORE (AP) _ Scientists say a device that releases lime into streams to combat the effect of acid rain appears to be reducing acidity for two to three miles downstream.

The question that remains is whether more fish eggs will survive.

''If we can improve streams for several years, we can allow the remnant species to improve or at least to maintain itself,'' Dr. Ronald Klauda, a Johns Hopkins University senior fisheries biologist, told The (Baltimore) Sun in a story published Monday.

This spring, Hopkins scientists began testing the idea of adding lime to neutralize acid rain in Maryland streams.

The idea was an extension of work done in the Northeast and Canada, where government officials have fought acid rain by liming acidic lakes. But buffering running water in a stream requires a new technology, one on which experiments have just begun in this country.

If follow-up tests to the Hopkins work prove conclusive, the scientists say liming could be a temporary solution to streams affected greatly by increased acidity.

The device is called a lime doser, a large, round concrete structure that perches on the edge of a stream.

When it rains, the doser sends measured amounts of a calcium and water mixture into the stream, making the stream more hospitable for fish.

Two lime dosers were placed in Maryland streams in 1986. They were computer-powered and cost about $40,000 each, too expensive for Maryland to use in great numbers.

But the new lime doser, placed on Stocketts Run in the Patuxent River, is a new design that doesn't rely on a computer. This version, costing $10,000 to $15,000, is the first to be put in a stream in the United States, Klauda said.

In some cases, the fish larvae below the doser had a significantly higher survival rate, but in other cases it was only marginally better, Klauda said.

''We don't know if they make a clear-cut difference in the survival of eggs and larvae,'' he said.

''It might well turn out that for a few key streams still in good shape or for streams that are trying to be restored, this approach would work,'' said Michael Hirshfield, director of the Chesapeake Bay research and monitoring division of the Maryland Department of Natural Resources, which helped fund Klauda's research with Living Lakes, a not-for-profit group funded by utility companies.

A survey last year found that at least 10 percent of the state's rivers have acid levels that kill fish larvae under laboratory conditions.