A midwestern commercial testing laboratory, which is under federal investigation for alleged irregularities in its test data, did at least 26 important investigations of chemicals approved for marketing by the Food and Drug Administration, according to federal records.

Industrial Bio-Test Laboratories Inc., of Oak Brook, I11., performed the tests on chemicals submitted to the FDA for approval by various manufacturers. FDA officials estimated yesterday that the chemicals may have made their way into hundreds of food additives, food colors and other industrial products that come into contact with foods.

IBT is under investigation by the FDA, the Environmental Protection Agency, the National Cancer Institute and several other federal agencies that require manufacturers to submit independent test data with products to be approved.

Last month Secretary Joseph A. Califano Jr. ordered the Department of Health. Education and Welfare to suspend all of its dealings with the laboratory after reports of alleged misstatements, misrepresentations and omissions of data from some of IBT's drug studies.

According to FDA documents obtained by The Washington Post under the Freedom of Information Act. IBT was involved in testing 45 chemicals submitted by various manufaturers for FDA approval since 1970.

Knowledgeable sources said yesterday that FDA investigators had found that IBT's tests were critical for the "regulation" - or approval - of 26 of the chemicals. The regulated chemicals appear in such items as fruit-flavored beverages, flavoring for hops and various food packaging and processing procedures, according to FDA records.

While the FDA investigators did not say that any of the agency's approvals were based on faulty information. an internal departmental memo has recommended that the regulatory agency go back and closely examine IBT's original laboratory data.

According to FDA officials, the agency does not normally receive specific laboratory data but receives instead a final manufacturer's petition based on the data. Last month IBT officials acknowledged to federal investigators that some of the company's testing data had accidentally been shredded.

IBT is a wholly owned subsidiary of the Nalco Chemical Co. Nalco was one of the several chemical firms whose petitions for approval of chemicalswas approved by the FDA.