Bradley D. Belt today announced his resignation as executive director of the Pension Benefit Guaranty Corp., effective May 31. Mr. Belt submitted a resignation letter to President George W. Bush. In an interview this afternoon, Mr. Belt said he has not made specific plans but will explore opportunities in the private sector. He said he is still focused on the work to be done at the PBGC in his remaining two months at the agency. Labor Secretary Elaine L. Chao will select Mr. Belt's replacement. Gloria Della, a Labor Department spokeswoman, was unable to provide information about a replacement.