DEBORAH YAOThe company that oversees much of the advertising for General Motors Corp. said Friday that the automaker owes it $50 million, an amount that could grow if GM's international subsidiaries also file for bankruptcy protection. The amount that Interpublic Group of Cos. disclosed in a regulatory filing is more than triple the $16 million listed in the bankruptcy filing GM made Monday. That's because IPG has yet to bill GM for some projects just completed or still in progress. Interpublic is one of GM's largest ad agencies. In turn, GM is one of Interpublic's largest clients and brings in around $350 million in business annually. Interpublic's Campbell-Ewald unit handles the Chevrolet brand while Deutsch has Saturn, one of the divisions GM is selling. McCann Erickson does work for Saab and, along with Deutsch, handles some GM corporate work. Interpublic is currently awaiting a court decision to be designated a "critical vendor," which could give it a better chance of recouping much or all of what's owed. Interpublic previously estimated that it could be owed as much as $150 million by GM. The disclosure of a much lower figure shows the agency has a good handle on its exposure to GM, said Barry Lucas, senior vice president of research at Gabelli & Co. Inc. in Rye, N.Y.