The Environmental Protection Agency announced yesterday it will seek nearly $7 million in fines against six major chemical companies that allegedly manufactured new chemicals without notifying the federal government.

The fines, ranging up to more than $3.7 million and involving some of the giants of the U.S. chemical industry, are the largest the EPA has sought under a provision of the Toxic Substances Control Act that requires firms to give the EPA 90 days' notice before producing or importing new chemical products.

The stiffest fine -- $3,756,000 -- would be levied against the BASF Wyandotte Corp. of Wyandotte, Mich. According to EPA officials, BASF Wyandotte manufactured two new chemical substances at its Holland, Mich., plant without notifying the EPA, and one of the chemicals had been put into extensive commercial use.

The EPA also is seeking a $1,436,000 penalty from BASF Systems Corp., an independent sister company to BASF Wyandotte, for similar violations. Other companies cited in yesterday's announcement, and their proposed penalties, are the Ciba-Geigy Corp. ($1.54 million), Union Carbide Corp. ($212,500), Dow Corning Corp. ($7,500) and Tremco Corp., a subsidiary of B.F. Goodrich ($6,000).

EPA officials declined to identify the chemicals involved, saying the law gives companies the right to keep that information confidential.

Although the agency has fined companies for similar reporting violations in the past, these penalties are far higher than it has proposed before. According to an EPA official, the highest fine proposed previously was $800,000, and the case was settled for $139,000.

But the action comes at a time of intense interest in chemical production practices, largely prompted by a disastrous chemical leak at a Union Carbide pesticide plant in Bhopal, India, in December that killed more than 2,000 people.

The fine is the second major penalty the EPA has sought in recent months against Union Carbide. Earlier this year, the EPA announced it would seek a $3.9 million fine against the firm, contending that Union Carbide had failed to report that one of its products caused cancer in laboratory animals.

Yesterday, the EPA said that Union Carbide had failed to notify the agency it was producing a new chemical at its Sisterville, W.Va., plant. The chemical was used commercially even though Union Carbide had reason to know it was in violation of the law, EPA said.

EPA officials said the violations by Union Carbide and Ciba-Geigy were detected by agency inspectors and disclosed voluntarily by the other four companies.