A federal bankruptcy judge has granted Wheeling-Pittsburgh Steel Corp. another extension during which only the company's management can file a plan for settling the company's debts. Judge Warren W. Bentz made the decision over the objection of the Pension Benefit Guaranty Corp., Wheeling-Pittsburgh's largest creditor, with a claim estimated at $500 million. The PBGC is a federal agency that insures company pension plans. Bentz invited the PBGC to petition the court to liquidate Wheeling-Pittsburgh under Chapter 7 of the U.S. Bankruptcy Code if the PBGC was convinced that the company could not successfully complete its 2 1/2-year effort to reorganize under Chapter 11. The PBGC declined.