Acid rain may kill fish, but it doesn't hurt yields of most food crops and actually helps as many as it hurts, according to the findings of a new study by the Environmental Protection Agency.

Tomatoes and strawberries, which thrive in acid soil naturally, were the happiest under artificially acidic drizzle given them by scientists at EPA's Environmental Reserach Laboratory in Corvallis, Ore. Carrots, beets and radishes did poorly, losing up to 50 percent of their normal yield. Grain crops were largely unaffected.

More than half the crops suffered leaf damage, which generally did not affect yield weight but rendered lettuce, spinach and mustard green crops unmarketable.

That finding came as something of a surprise, according to bioligist Jeffrey J. Lee. "We had thought there might be a close correlation between foliar [leaf] injury and crop yield, but the results show there is not," he said. "Of course, yield and marketability are two different things."

Congressional hearings were held recently on acid rain, which is formed when sulfur dioxide or nitrogen oxide air pollutants mix with moisture in the air.EPA and Congress are considering ways to deal with acid rain, reportedly, the killer of all fish and plant life in hundreds of lakes in the northeastern United States and Canada.

However, the formative process of acid rain is little understood. Electric utilities and other industries have installed millions of dollars worth of pollution-control equipment already and are certain to resist any tightening of the standards for oxide emissions.

Lee and researchers Grady E. Neely and Shelton C. Perrigan set out to learn about the damage that varying degrees of acidity can do, and to see which crops were mostly vulnerable.

They raised 28 vegetables and grasses in pots, subjecting them to three different strengths of artificial acid rain, for a total of 84 test plants. Of those, 62 plants showed no significant difference in yield from control plants grown under neutral rainwater, while 11 plants increased their yeilds and 11 plants reduced theirs. But 46 plants, or 55 percent of the test sample, suffered leaf damage, including all the leafy crops.

Acid levels are measured on the pH scale, on which 1 is a very acidic, 5 is neutral and 10 is very alakline. Normal rainwater has a pH of 5.6. Prevailing winds carry sulfur dioxides eastward from the Ohio River basin and elsewhere, however, so that "in the northeastern United States, pH 3.5 is typical of summer rains," the EPA study said. That is about the acidity of lemon juice, and "more acidic rains do occur," EPA reported.

The team used simulated sulfuric acid rains of pH 4, 3.5 and 3.0 for its tests.

Grain crops seemed to be the toughest, suffering neither leaf damage nor significant yield loss at any level of exposure. Corn increased its output by 13 percent under pH 3.0 rainfall, one of the curious zigzag results that showed slightly negative effects at one acid level and positive effects at another.

Strawberries increased their weight by 51 percent under the weakest pH 4 acid level, jumping 72 percent under the lemon-like pH 3.0. That also produced a 31 percent heftier tomato crop, 24 percent more timothy grass and 23 percent more orchardgrass. Green peppers increased 31 percent under pH 3.5 water, but the yield dropped back at pH 3.0.

Carrots lost nearly half their weight at the highest acid levels, as did beets and radishes. Some of the radish findings were confused by a plauge of snails and beetles that ate many of the control plants but ignored the acid-watered ones, an event that Lee said merited further study.

Potato crops were down 14 percent at pH 3.0 but unchanged in weaker acid rains, while mustard greens were down at weak level, up to normal under pH 3.5 and down fully one-third at the top acid rate.

The only valid generalization emerging from the study, were these: plants that sprout with two leaves (dicotyledons), like carrots and spinach, were far more effected than those that sprout with one (monocotyledons); and the reserachers did not know how to grow soybeans or peanuts.

"The peanuts just didn't grow well even in the controls," Lee said. "Maybe we ought to ask President Carter for advice."