WASHINGTON (Reuters) - U.S. President Donald Trump will pick former Virginia Attorney General Ken Cuccinelli as the head of the U.S. Citizenship and Immigration Services, the Washington Post reported on Friday.

Cuccinelli will replace L. Francis Cissna as the head of the agency, which manages the country's legal immigration system. Cissna told staff in a farewell letter on Friday he had resigned at the president's request, effective June 1, a USCIS official said.

The White House is still figuring out what exactly Cuccinelli will be doing in his new role, the Post reported. A White House official did not immediately respond to a request for comment.

As Virginia's attorney general and a state senator, Cuccinelli developed a reputation as a hardliner.

In Virginia, he called for denying citizenship to U.S.-born children if their parents are in the country illegally, introduced a proposal barring unemployment benefits to people who were fired from jobs for not speaking English and authorized law enforcement officials to investigate the immigration status of anyone they stopped.

Cuccinelli will likely face a pitched battle for the Senate approval of his nomination, though it is controlled by Trump's Republican party.

Cuccinelli heads a political group that has clashed with Senate majority leader Mitch McConnell, who has vowed to block Cuccinelli from being confirmed for any administration position, according to media reports.

He is also unlikely to receive much support from Senate Democrats.

In April, Homeland Security Secretary Kirstjen Nielsen announced her departure from the Trump administration, raising the specter of more firings of senior immigration officials.

Trump is seeking to overhaul the U.S. immigration system and has sought to crack down on illegal immigrants, but has been largely unable to enact the sweeping changes he has sought.

Cuccinelli met with Trump on Monday and was expected to be picked for an immigration policy position by the president.

(Reporting by Makini Brice, Yeganeh Torbati and Roberta Rampton in Washington; Editing by Matthew Lewis)