The nation's largest makers of ready-to-eat cereals said yesterday that a government victory in the Federal Trade Commission's antitrust suit against the industry would be a damaging blow to American industry based on misguided economic theory.

The record in the FTC's case "consists of nothing more than baseless accusations conjured up to support a now-discredited economic theory," Kellogg Co. said in the final regulatory volley in the case. Kellogg is one of three companies charged with controlling the industry through a "shared monopoly." General Mills Inc. and General Foods Corp. are the other two targets of the action.

General Foods, in a final brief filed with the FTC, charged that a "finding of conspiracy in this case would result in the wholesale condemnation of much of American industry, a result obviously not intended by Congress in the passage of the antitrust laws."

The statements came as the record closed in the eight-year-old case, which has been the target of considerable political criticism, including a statement last Oct. 29 by then-presidential candidate Ronald Reagan. Reagan said the case "has very little basis in fact." If the FTC were to order the breakup of the three cereal companies, the ruling "would have a chilling effect on American industry," Reagan said then.

A congressional review of FTC antitrust powers also is expected this year, with the cereal case likely to be a major part of such a probe.

An FTC law judge is expected to issue an initial decision in the case by Nov. 1. The commission then will evaluate that decision.

The FTC has charged that the alleged monopoly among the companies cost consumers more than $1.2 billion in higher grocery store prices between 1958 and 1972 alone. The commission's complaint seeks to split off certain facilities of the companies and institute a licensing procedure of certain cereal brands.