Mary Carter Paint Co., Tampa, will acquire the National Biff-Burger System, Inc., of Largo, a chain of franchised drive-in restaurants operating in four states and Toronto, Canada, it was announced yesterday by L.G. Davis Jr., president of the paint company.

Davis said the acquisition represents his company's first step in a plan to diversify its franchise chain operations in fields other than paint. "We're supplementing but not supplanting a continuing program to expand our strong position in manufacturing and retailing paint and related do-it-yourself items," Davis said.

Mary Carter has grown from 29 retail paint stores in 1955 to more than 850 through franchise of sales and service.

National Biff-Burger includes 26 drive-ins in Florida, North Carolina, Indiana, Virginia, and Toronto, specializing in limited menu, minimum cost food items, according to Bruce Brane, who has been president of the chain and who will become a part of Mary Carter management.

The acquisition will involve and exchange of shares in excess of $500,000.

In the first six months of 1962, Mary Carter reported net income of $741,013, or 33 cents a share, on 2.2 million shares outstanding, as against $546,323, or 24 cents a share on 2.2 million shares outstanding during the comparable period of 1961. Sales in the six months ended June 30, 1962, were $9.6 million compared with $9 million in the similar period a year previous.