Mrs. Baird's Bakeries Inc. today became the first company charged in a nationwide investigation of possible price-fixing and bid-rigging in the wholesale bread industry.

The company and some of its top executives are the subjects of three investigations by prosecutors into possible price-fixing of certain agricultural products.

The shareholders say their objections have deepened since Archer-Daniels disclosed in June that it was being investigated by Federal prosecutors for possible price-fixing.

The unusual collaboration by the two longtime archrivals, lawyers said, could figure into a prosecution for possible price-fixing and other collusive practices under study by the Justice Department.

For three years Federal antitrust prosecutors have been questioning a wide array of art world figures about possible price-fixing and collusion in the famously secretive multibillion- dollar art world.

For last week it turned out that Mr. Whitacre, working with the F.B.I., secretly taped executives' conversations as part of an inquiry into possible price-fixing.

Agriculture Secretary Dan Glickman has asked the Justice Department and the Federal Trade Commission to look into possible price-fixing or anticompetitive pricing by meatpackers.

They include a fraud investigation involving corporate money some executives received in overseas bank accounts as well as several inquiries into possible price-fixing involving several agricultural products.

The Whitacre case is significant for several investigations involving Archer-Daniels, three involving possible price-fixing at the company and the fourth relating to money obtained by a number of executives involving foreign bank accounts.

The Justice Department has been investigating Archer-Daniels and at least three other milling companies for possible price-fixing of high-fructose corn syrup and other corn products.