As F.B.I. director, James B. Comey had widespread support from his agents, according to internal survey data released Wednesday that contradicts President Trump’s claim that he fired Mr. Comey in part because agents had lost confidence in him.

Mr. Comey’s firing is among many topics now under investigation by the Justice Department special counsel, Robert S. Mueller III. Mr. Trump and his aides have offered changing explanations for why he fired Mr. Comey, who was overseeing the investigation into Mr. Trump’s associates and possible links to Russia’s election interference.