Three potential buyers are now interested in taking CompuServe Corp off the hands of its owner H&R Block Inc, with investment firm Welsh, Carson, Anderson and Stowe once again tipped as the front runner by the Wall Street Journal. Under the proposed deal, Block would be likely to retain a minority interest. But America Online Inc is also said to have made a renewed offer, and ambitious WorldCom Inc, the telecommunications company which owns internet service provider UUNet, is also thought to have put in a bid.