Before rejecting a compromise with teachers that would have won New Jersey a $400 million federal education grant, Gov. Chris Christie’s main objection was that it would appear that he had given in to the teachers’ union, a former education commissioner testified on Thursday.

The governor, who had battled the union all year, said “that he was not going through the fire with all of their attacks on him merely to cave in to the union,” the former commissioner, Bret D. Schundler, told a State Senate hearing investigating the loss of the federal grant. “And he said that emphatically and for a rather extended period of time.”

Mr. Schundler recalled that in his conversation with the governor, in May, he had explained that it was the union that had given ground, and that the administration had won nearly everything it wanted. “When the governor came to understand that, his concern became more about how it would be perceived,” he said.

Michael Drewniak, the governor’s press secretary, said that Mr. Christie had rejected the plan because it “fell far short of the education reforms the governor has long endorsed.” He dismissed the hearing on Thursday, which had been convened by Democratic lawmakers, as a “political circus.”