R. J. Reynolds began its offer for Nabisco Brands.

The company said it began an offer of $85 a share in cash for 29 million shares, or 51%, of Nabisco Brands’ stock. R. J. Reynolds Industries proposes to acquire the remaining stock with securities valued at $85 a share. The offer, unless extended, is scheduled to expire July 1. The merger agreement was announced Sunday and has been approved by the boards of both companies. It is subject to government antitrust clearance and approval by shareholders of Nabisco Brands. The merger, valued at about $4.9 billion, will create the nation’s largest food and consumer-products company.