DALLAS – The leader of the pilots’ union at American Airlines resigned Thursday after pilots rejected a concessionary contract offer that he supported.

David Bates said that the union’s board asked him to step down and he agreed.

Bates supported ratification of a company offer to give pilots pay raises and a 13.5 percent stake in the company after it emerges from bankruptcy protection. He portrayed it as the best deal possible under difficult circumstances. But 61 percent of pilots voted to reject the offer, which contained outsourcing provisions that they opposed.

After the vote, American indicated that it will ask a federal bankruptcy judge to impose terms of an April offer that included smaller pay raises and no stock in the new company for pilots.

“Although I believe that ratifying the tentative agreement would have been the best course for our pilot group, the majority of our pilots signaled their preference for taking a different path,” Bates said in a message to union members. “Given these circumstances, I concluded that continuing to serve as your president was not in the interests of the pilots.”

Vice President Anthony Chapman, 53, was elevated to acting president of the Allied Pilots Association until the board picks an interim leader for the rest of Bates’ term, which runs through next June.