The owner of Super Fresh said it was trying to buy Pathmark Stores Inc. in a deal that would join two supermarket chains that have been losing market share in the Philadelphia region.

The Great Atlantic & Pacific Tea Co. Inc., of Montvale, N.J., said yesterday that it was negotiating an offer of about $12.50 a share for Pathmark, a price that values the Carteret, N.J., retailer at $653 million.

On a dismal day for stocks, traders were pleased with the possible deal between the Northeastern supermarket operators. Great Atlantic's shares gained $2.30, or 7.45 percent, to close at $33.17 on the New York Stock Exchange. Pathmark's shares lost 10 cents to close at $11.95 on the Nasdaq.

Equity analysts and other industry observers have speculated for years that Great Atlantic and Pathmark would make a good match geographically and because both companies are unionized. Nonunion chains usually stay clear of union chains.

Great Atlantic operates 410 stores, most in the region from Connecticut to Maryland, including 35 Super Fresh locations and three Food Basics stores in the Philadelphia region.

Pathmark has 140 stores in Pennsylvania, New Jersey, Delaware and New York, including 26 in the Philadelphia region.

Pathmark's largest shareholder is the Yucaipa Cos. L.L.C., a Los Angeles private-equity firm run by billionaire Ron Burkle. Burkle's company is also the largest shareholder in Wild Oats Markets Inc., which has a deal to be acquired by Whole Foods Market Inc. for $670 million.

Contact staff writer Harold Brubaker at 215-854-4651 or hbrubaker@phillynews.com.