GRANTS PASS, Ore. (AP) — A federal auditing agency has upheld a challenge to a U.S. Forest Service contract for two next-generation air tankers to fight wildfires. But what that means for the federal air tanker fleet this summer is not yet clear. Competing air tanker companies objected to a sole-source contract the Forest Service awarded to Neptune Aviation Services in Montana. It would be worth $496 million over nine years. The Government Accountability Office said Wednesday the Forest Service should either bolster its justification for considering just one company or redo the bidding. Forest Service spokeswoman Jennifer Jones says the agency is evaluating that choice. She says the agency still has 10 large air tankers ready for fire season, including two of the next-generation type that fly faster with bigger payloads of fire retardant.