The Treasury Department's top official on domestic finance matters plans to resign at the end of the current session of Congress.

Randal Quarles, who has been the point person in pushing the administration's efforts to reform mortgage giants Fannie Mae and Freddie Mac, said in a resignation letter to President Bush Thursday that after five years in the administration, he wanted to return to the private sector.

Before becoming undersecretary for domestic finance, Quarles served during Bush's first term as assistant Treasury secretary for international affairs.

In that position, he helped develop the administration's response to Argentina's 2001 debt default and efforts to push China to revalue its currency as a way of dealing with America's huge trade deficit.

In his resignation letter, Quarles said that "the burdens of this lengthy public service on my family have been great" and it had been his intention to leave the administration around the time of the 2006 congressional elections.

Quarles served under all three of Bush's Treasury secretaries — Paul O'Neill, John Snow and the current secretary, Henry Paulson.

Paulson saluted Quarles for playing "a major role in an unusually broad range of matters — from the Argentine debt default to terrorism risk insurance and from Chinese currency flexibility to GSE reform," a reference to the administration's efforts to impose greater regulation on Fannie Mae and Freddie Mac.

Treasury spokesman Tony Fratto said Quarles had made no decision on what he planned to do after leaving Treasury.