In the Adirondack Mountains is a crystal jewel of a lake, so clear that anyone can see there are absolutely no fish in it.

Neither are there any algae, nor do any frogs sing on the banks. It is a mockery of its name, Brooktrout Lake, for it has been sterilized by acid rain. At least 90 and perhaps 200 more lakes in upstate New York, and another 140 in Canada, are equally pure and dead.

In Washington, acid rain is calling into questions the very structure of the Clean Air Act of 1970. This rain, occasionally as acid as vinegar, is one product of the sulfur oxides and nitrogen oxides that come out of utility and industrial smokestacks and out of automobile exhausts. When the oxides mix with water in the atmosphere, the result is weak forms of sulfuric acid and nitric acid.

Where these rains fall, fish die. First the baby fish go, especially in the spring when melting snow pours a season's worth of stored-up acid into lakes and rivers. Ironically, the first major sign of trouble is a fisherman's delight -- a catch of exclusively older and bigger fish.

The Canadian government estimates that fish in 48,000 lakes are in danger of extermination in the next 20 years if something is not done. Salmon fishing is all but wiped out in southern Norway and Sweden, where acid rain as first identified in 1971. Japan has a serious problem.

In United States, alarming acidity levels have been found not only in the Adirondacks of New York but in Minnesota's Boundary Water Wilderness, in northern Wisconsin and Michigan, in San Francisco and Los Angeles and even in the remote Rocky Mountains.

"This is one of the most dramatic examples of a newly discovered problem that is not addressed by the Clean Air Act," said Sen. Gary Hart (D-Colo.), chairman of the National Commission on Air Quality.

As amended, the act sets limits for gunk levels in the air of a state or locality at ground level, where it is breathed. Emissions allowed each plant total won't exceed that level. But industries have found that a high smokestack can belch the sulfur dioxide high enough into the air so that winds will carry some or most of it out of the area.

The result is acid rain coming down hundreds or even thousands of miles away from the pollution source. The acid of Brooktrout Lake in New York, nine miles from the nearest road, probably originated in smokestacks in the Ohio River Valley.

Winds from Great Britain kill salmon in Norway.

Canadian and U.S. officials are negotiating a treaty to stop our great international pollution exchange: we send them an estimated 25 million tons of sulfur dioxide every year and they send us 5 million tons, according to a Canadian government study.

There is international worry that the problem will soon get worse because of the push toward coal. The Environmental Protection Agency has so far allowed 90 utility and industrial boilers to convert from oil to coal and has approved another 85 new coal-fired boilers for power plants. In each case the pollution control requirements have been an issue.

"Lots of states are coming in saying they have room to relax the requirements," said Robert Rauch of the Environmental Defense Fund. On paper, sulfur and nitrogen oxides appear to have been widely cleaned up, since the oxides that convert to acid rain in the atmosphere are never counted on the ground.

"That's how the law was designed," said David Hawkins, EPA's administrator of air, noise and radiation control. "It may well be time to seek changes in the Clean Air Act to give the government authority to do something about total emissions."

New plants are less of a problem than old ones, which often cough seven to eight times as much junk into the air. Yet the Clean Air Act exempts all plants built before 1970, when the law was passed, from the standards that apply to new plants. These were tightened in June to require utilities to eliminate 70 percent of all the sulfur from low-sulfur coal and 90 percent from high-sulfur coal before it is burned.

Yet by 1985, nearly 90 percent of all the sulfur produced in America will still be coming from those outdated power plant units, according to EPA estimates. Some of those are still not in compliance with the ground level standards, and it is here that the main battle is currently being joined.

"These plants have a tremendous incentive to increase the height of their smokestacks to disperse [the sulfur dioxide] high in the air," said Rauch of the EDF. "But that just transfers the problem downwind."

In Ohio far and away the state where the most coal is burned, raising the smokestacks at two mammoth power plants helped Cleveland Electric Illuminating Co. to argue successfully in June for an EPA relaxation of Ohio's pollution standards in their case. Ground-level sulfur dioxide would be reduced below the required limit by the new stacks, the company said, and so it won preliminary permission to burn high-sulfur Ohio coal without installing expensive scrubbers.

EDF will contest the ruling, as will the Sierra Club. "This is the big test case," said Rauch. "If we lose here, you'll see a domino effect with seven or eight other plants . . . emissions in Ohio will drastically increase."

The Cleveland Electric plants, called Eastlake and Avon Lake, on either side of Cleveland, will allowed to put out as much sulfur dioxide as all 13 plants of Consolidated Edison Co. in New York, Rauch said, and most of it will become acid rain.

Hawkins of EPA noted that the two plants never have been in compliance with the rules, so total emissions won't go up.

To the complaint that too many higher-stack construction permits are being issued too easily, Hawkins responded that law enforcer has to balance the possibility of victory against the extra work it creates for itself. "The case for additional control certainly appears now to be more pressing," Hawkins allowed.

Another pending suit involves EPA's decision last year to allow increased sulfur emissions with higher stacks at Monongahela Power Co.S Harrison plant in Fairmont, W.Va., and at Ohio Power Co.'s Mitchell plant in Moundsville, W.Va. "It may not cause a problem in Fairmount or Moundsville, but it causes an acid rain problem in southwest Pennsylvania," said Walter Zadan, president of the Group Against Smog and Pollution (GASP) in Allegheny County.

He said rainfall measured in the Allegheny National Forest in early 1978 was 3,000 times more acidic than normal rainwater -- "more acid than lemon juice." In terms of pH level the scientific measure of acidity, normal rainwater measures about 5.6, slightly more acid than a neutral 7. But the Allegheny rain came in at a pH of 2.3.

Any attempt to deal with acid rain immediately confronts the impossibility of tracing its origin. Then there is the question of who pays for cleaning it up. The Electric Power Research Institute (EPRI), the industry's research arm, argued at congressional hearings in May that too little is known yet to decide how to fight the problem.

There is so little agreement on the sources of acid pollution and on the extent of the problem that no one has ventured to estimate a cleanup cost, though the cost would clearly be immense.

Sometimes sulfur dioxide emissions are constant over an area but acid concentrations below vary widely. Some lakes are more acidic than very similar lakes nearby. Measurements to document the rise in acidity levels since the 1950s were often taken at different places. Most of the statistics are weak.

To remedy this, EPRI is doing a $7 million study that involves flying with a pollution plume all the way to Norway. EPA has a 10-year study at $10 million per year, but pressure is building to do something before the results are in.

"It's a political and legislative decision," said Hawkins. "It may well be one whose time has come."