An Environmental Protection Agency study has found that federal approval of more than 200 chemicals and pesticides now on the market was based at least in part on inadequate or falsified health safety tests.

The study focuses on about 1,200 tests of 212 chemicals conducted during the 1970s by Industrial Bio-Test Laboratories Inc. of Northbrook, Ill.

IBT, a subsidiary of Nalco Chemical Co., was once the largest private research laboratory in the country, but it stopped testing in 1978 after federal investigators began looking into its activities.

As a result of that investigation, four former IBT officials, including former president Joseph C. Calandra, are on trial in U.S. District Court in Chicago on criminal charges involving falsification of health test data on chemicals to obtain government approval for marketing the substances.

The EPA study, which has taken five years and is scheduled for release in mid-June, has found that virtually all pesticides and herbicides approved by IBT were subjected to at least one invalid test. It also has found that about two-thirds of the 1,200 individual tests cannot be considered reliable.

Many of the pesticides and herbicides, including Roundup, Captan, Orthene, Machete and Lasso, are widely used by farmers and gardeners.

Rep. George E. Brown Jr. (D-Calif.), chairman of the House Agriculture subcommittee that has held hearings on the EPA's pesticide program, said yesterday that the study raises serious questions about the safety of the 212 chemicals.

"The basic answer is that nobody knows if they are safe , including the EPA," Brown said. "The EPA cannot prove the chemicals are hazardous in the absence of the data, nor can the companies prove the chemicals are safe."

EPA sources said discovery of the flawed IBT testing will create a gap in the data and require new research, but they added that many of the chemicals were also studied by companies other than IBT.

Tom Slocum, a spokesman for Monsanto Co., said most of his company's major products were tested, at least in part, by IBT. Many Monsanto products are on the EPA list, including the herbicides Roundup and Lasso.

Slocum said Monsanto has conducted new tests to prove the products are safe.

"The concerns about IBT are not new," he said. "Monsanto and many other companies have worked for years to repeat key tests. There's enough information in the data base to support registration federal approval ."

The federal investigation of IBT began in 1976 when the company was under contract to most of the nation's major chemical companies for studies of the health effects of chemicals and drugs as required by EPA, the Food and Drug Administration, the National Cancer Institute and the Army. IBT clients included Dow, Monsanto, DuPont, Velsicol, Chevron and Ciba Geigy as well as Nalco, its parent company.

FDA investigators raised questions about IBT when they discovered studies showing that the same rat had died several times, sometimes from different causes.

"We reviewed all the IBT studies . . . to see if any were crucial to approvals we had made, and most were not," FDA spokesman Bill Grigg said yesterday.

He said the two most serious cases of data falsification involved testing of Naprosyn, an arthritis drug, and TCC (trichlorocarbonilide), a substance used in deodorant soaps. After further testing by other companies, both are still on the market

The IBT officials, including Colandra, Moreno L. Keplinger, Paul L. Wright and James B. Plank, were indicted in 1981 for concealing test results in four major studies, including Naprosyn, TCC, the herbicide Sencor and the pesticide Nemacur.