Some members of Congress are disputing a claim by Defense Secretary Robert Gates that splitting a contract for aerial refueling tankers would cost U.S. taxpayers an extra $7 billion. Rep. Neil Abercrombie, D-Hawaii, who chairs a key appropriations subcommittee, said tankers proposed by both Boeing Co. and Northrop Grumman Corp. are based on existing models, helping to keep development costs down. Industry sources, too, say the Gates figure is hard to justify. "We are scratching our heads," an industry insider told Reuters. "We don't know where that figure came from."