CHICAGO, March 5 (Reuters) - A United Airlines flight carrying 176 passengers and a crew of seven underwent an emergency evacuation on the tarmac after landing at O'Hare International Airport on Tuesday when a warning light indicated the plane's brakes had overheated, the airline said. There were no injuries. The Boeing 767's pilot halted the plane on a taxiway after an instrument panel light indicated a brake problem, a spokesman said. It was not known if there was a malfunction or whether the signal light was faulty. The flight originated in Phoenix.