An environmental group has a sharp pin poised over the Environmental Protection Agency's so-called "bubble" policy, accusing the agency of letting industries play a shell game with their pollution to the detriment of the air.

The bubble policy was designed to give industry more flexibility in meeting air pollution standards. In essence, it permits industries to expand and add new sources of pollution if they can reduce pollution from existing sources by an equal or greater amount.

But the Natural Resources Defense Council says it has found "very serious problems" with a half-dozen bubble applications it has examined, including some that involve "clear violations of the law and gross 'funny business' with the emissions calculations." Two of the applications have since been disapproved; the other four are pending.

In a letter this month to Joseph A. Cannon, associate EPA administrator for policy, NRDC attorney David D. Doniger complained that an application filed by B.F. Goodrich for its Avon Lake, Ohio, chemical plant is "seriously flawed" because it uses a "bogus credit calculation."

Rather than clean up emissions from two boilers at the plant, Goodrich has asked to be allowed to take a credit against the emissions from three polyvinyl chloride silos.

According to Goodrich, the silos are emitting about .05 pounds an hour of particulates, but, the firm said, the state's clean air plan permits as much as 8.6 pounds an hour. Thus, Goodrich said, it should get a credit of 109.8 tons a year, enough to cover its belching boilers.

The NRDC cried foul, pointing out in comments to EPA's Chicago regional office that the plant is located in an area that has not met Clean Air Act standards for particulate emissions and instead should be reducing emissions through the use of "reasonably available control technology." If Goodrich's controls are able to reduce emissions to .05 pounds an hour, the council argues, that should be the plant's baseline.

But Mike Levin, head of the EPA policy office's regulatory reform staff, said Goodrich's application is under review at the agency, but "we're not at all sure there's anything wrong with it."

Doniger also cited two applications filed by the Monsanto Co. in the Houston area. In one, the chemical company wants to take credit for reducing emissions at a facility it shut down and dismantled two years ago. In another, the company's application claims 200 tons a year in emission reductions from a facility, even though EPA records show it historically has emitted less than the levels cited by the firm.

A Union Carbide application in the same area seeks credit for a facility that has been closed for four years, according to Doniger.

Cannon said the agency has approved more than 30 bubble applications, has 150 applications under consideration and "obviously is concerned" about whether "bubbles are getting through that are bad bubbles."

"No one wants that," he said. "We're trying to police as best we can but, well, some people rob banks."

He said, however, that the central question raised by Doniger's letter was whether state clean air plans, which are required under the Clean Air Act, are adequate. "That's not relevant to the bubble," Cannon said. "Our position is that the bubble is a neutral policy."

Doniger conceded that the NRDC is concerned about the adequacy of state air plans, but he contended that EPA could use the bubble policy "to induce cooperation" and get states to tighten their plans.

Levin responds that the bubble policy wasn't intended to be a "privilege" but is an "essential tool" that can provide immediate, interim benefits while areas move toward compliance with clean air standards.

"Nobody would have any trouble with air pollution control if it didn't cost a lot to do it," Levin said, contending that giving industries credit for emissions below allowable levels is a proper reward for "doing something extra."

Over the last several years, the bubble policy has earned a measure of approval from environmental groups. In February, for instance, the addition of a bubble provision helped cement a compromise between environmentalists, industry and the government on a regulation governing the amount of toxic wastes the steel industry is permitted to discharge into rivers and streams.

But the NRDC, in its comments to the Chicago EPA office, warned that the EPA's "willingness to close its eyes to tainted bubbles cannot go on much longer before the bubble concept itself will earn a tarnished reputation."

Its reputation already has become somewhat tarnished in the eyes of environmentalists over the past two years, as a result of several proposed changes in the policy and its application.

In October, 1981, the EPA issued new rules defining the term "source" to include an entire plant, rather than each boiler, smokestack or pipe that might emit pollutants. Then in April, 1982, the agency announced a policy that would expand the bubble concept to new sources in areas not in compliance with clean air standards.

The courts have overturned the October rule, but an appeal is pending at the Supreme Court.

A bubble-like remedy that the EPA recently approved for the General Motors Corp. to help it avoid a costly recall also has provoked sharp criticism and a lawsuit.

Last July, the EPA agreed to let GM avoid recalling nearly 700,000 1979 Pontiacs that failed to meet federal emission standards. In return, GM agreed to "offset" the emissions by producing 2.3 million cars that would meet a tighter-than-required emission standard.

NRDC and the Center for Auto Safety have joined in challenging the agreement, contending that it reduces the incentive for auto manufacturers to build durable emission-control systems.