By advising and financing United Rentals Inc.'s hostile bid for a competitor, Goldman, Sachs & Co. is fueling a debate over its mergers and acquisitions strategy.

For as long Goldman's rivals can remember, the firm has had a clear policy when it comes to advising bidders in hostile takeover attempts: Stay away. But some observers say the United Rentals mandate-coming on the eve of Goldman's planned initial public offering-suggests that the firm's strategy may be changing.

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