The Environmental Protection Agency yesterday took its "best shot" at controlling the nation's flood of toxic waste, issuing regulations to define it and say how it must be handled in the future.

But critics immediately charged that EPA had already missed the mark by exempting far too many small waste generators and leaving too many chemicals out of the rules.

Eckardt C. Beck, EPA's assistant administrator for water and waste management, said the rules, a stack eight inches high, were probably the most complex the U.S. government had ever put together. They cover 501 hazardous chemicals, wastes and waste processes and will cost industry about $1 billion to implement, Beck told a news conference.

But the costs are small compared to the price of doing nothing, he added: for example, it is now estimated that it may take $124 million to clean up the abandoned Love Canal site in New York.

"This is our best shot at trying to curb the hazardous waste problems of the future and to begin to sensibly manage the problems of the past," Beck said. In a statement, EPA administrator Douglas Costle predicted that the new procedures to track the wastes "will turn up information and situations which will shock our nation" regarding past practices.

Covered under the rules are 40 million of the estimated 57 million metric tons of residues that are the price Amaerica must pay, Beck said, for a society of plastics, chrome and wash-and-wear clothing. This, he said, is "a substantial bite of the apple" and "a pretty bold step," but promised that coverage will be expanded over the next several years.

President Robert Roland of the Chemical Manufacturers Association responded that EPA had underestimated the costs and the difficulties of compliance industry faces. "They have not addressed some of the real issues," he said.

Roland complained that the requirements "go well beyond the state of the art" of waste disposal in lumping wastes of varying hazard together for identical high-level treatment. "That could mean you'll be out of dump sites," he said.

On the other side, David Lennett of the Environmental Defense Fund objected to the exemption from the rules of any firm producing less than 1,000 kilograms (2,200 pounds) of hazardous material per month. EPA originally proposed to exempt levels of 100 kg. per month, but raised the exemption tenfold after howls of pain from small producers.

In response to questions, Beck defended the shift, saying that while the exempted companies may be 91 per cent of the waste producers, they are sources of only 1 percent of the targeted waste. "We honestly felt it would be best to put our efforts on the large volumes . . . and also to relieve ourselves of a tremendous amount of administrative trivia," he said.

In addition, he said, EPA had picked 118 of the most "acutely toxic" chemicals and will require control of any amount over one kilogram (2.2 pounds) per month.

But Lennett and critics in the EPA were not mollified. One percent of 57 million metric tons is still 1 billion pounds of toxics per year, he noted. In addition, EPA's lists of chemicals to be regulated leave untouched 65 percent of potentially hazardous waste types, he said. The agency also leaves it up to each firm to label itself a hazardous waste producer and EPA does not require confirmatory test results, he said.

"It took 3 1/2 years for EPA to develop these regulations. I can't say that it has been worth the wait," Lennett said.

The rules have been pending since the 1976 passage of the Resource Conservation and Recovery Act (RCRA), which set out to control toxic residues. The Environmental Defense Fund obtained a court order last year requiring EPA to issue the regulations, but they were held up again lst week in a policy battle with the Office of Management and Budget.

OMB is concerned that the new regulation may impose an unreasonable paperwork burden on industry, adding 5.2 million hours of labor per year, and has given waste-producing firms 15 days in which to comment.Then OMB has the option of requiring changes in the forms that must be kept by the companies and will announce any changes by June 15. The entire system goes into effect Nov. 12, Beck said.

Yesterday's requirements cover three basic areas:

There are lists of wastes, waste sources and industrial waste processes whose products will be considered hazardous under the law. If a substance is toxic, can be ignited at 140 degrees Fahrenheit, or is corrosive or explosive, it is included in the 416 chemicals and 85 processes named yesterday. Twenty-five waste processes will be outlined May 30 and another 49 in the fall.

There are general requirements for facilities that treat, store or dispose of hazardous wastes. All of them must apply for an identification number within 90 days and begin assessing the wastes they handle for danger and treatment needs.

Each site eventually must install groundwater monitoring systems and provide regular inspections, security and employe training. Interim status will be given to all those that register and promise to upgrade facilities, which may take up to 10 years.

There are outlines for state-level programs that will hahve to be "equivalent to and consistent with" federal aid, to draw up their own plans, which may be stiffer than EPA requirements but no looser.

A manifest system to track the wastes from generator through transporter to an ultimate grave was announced in February and also goes into effect in the fall.

Hugh Kaufman, EPA's program manager for hazardous waste damage assessment and an outspoken critic of his agency, said it was not clear to him that regulations expected in the fall will fill the gaps in current regulations.

Although yesterday's rules require groundwater monitoring at a waste treatment site, for example, the standards that the measurement must meet will not be set until October, if then, Kaufman said. He said internal memos had been circulated, advising attorneys to specify that EPA "expects to issue" such standards, rather than that the standards would definitely come out.

"We could have promulgated California's regulations and save a lot of paper," he said.

Beck maintained that the new regulations are a good start on a vast problem. "Is this where we want to be 10 years from now? No, but it's a giant step forward," he said.