WASHINGTON, April 9 (Reuters) - White House economic adviser Kevin Hassett said on Thursday that he was confident Kevin Warsh would start as Federal Reserve chairman in May and that he did not expect current Fed chairman Jerome Powell to remain on the board.

"I'm highly confident that that will happen," Hassett told Fox Business Network, adding that he believed a confirmation hearing for Warsh was on track to begin next week.

Hassett said Powell had indicated he would leave the central bank once a new chair was selected.

"He's really signaled that once there's a confirmed head chair, that he'll step aside, and that's the appropriate thing for him to do," Hassett said on the "Mornings with Maria" program.

However, Powell said in March he would not leave the Fed at least until a criminal investigation spearheaded by U.S. Attorney Jeanine Pirro is over and that he had not yet decided whether to remain in a governor's seat on the central bank's board that lasts until 2028.

Powell's term as Fed chief ends in May.

A U.S. judge last week upheld a block on subpoenas issued in the investigation into Powell, setting up a likely appeal that could further delay President Donald Trump's move to install a more compliant central bank head.