Three of the largest newspaper groups in the United States are in talks to set up a network to sell advertising jointly on their newspapers’ Web sites.

The Wall Street Journal reported last month that Gannett Co., McClatchy Co. and Tribune Co. are planning to offer advertisers “one-stop shopping” for display ads on Internet sites.

The project, code-named Open Network, is an effort to woo national advertising from big advertisers like car manufacturers and phone companies.

The three publishers already cooperate through the online employment Web site CareerBuilder. 

This new project comes as Yahoo Inc. and Monster.com court newspapers in a bid to grow online classified employment revenues.