James B. Lockhart, the regulator for Fannie Mae (FNM) and Freddie Mac (FRE), is stepping down, providing an opportunity for the Obama administration to put its own stamp on the future of the troubled firms.

Lockhart, who headed the Federal Housing Finance Agency during the government's dramatic seizure of Fannie and Freddie last fall, said he had chosen to leave now, at the one-year anniversary of the creation of the new agency. He said he had been speaking with administration officials over the last four months about an appropriate succession.

"To be perfectly honest I think they would like me to stay around a little longer," he said in an interview Wednesday.

It is unclear whom the Obama administration will select to become the agency's director. That person is poised to play a key role in deciding the future of the companies, something the administration has yet to spell out. The White House has said it will unveil a plan for Fannie and Freddie when it releases its 2011 budget in February.

Proposals include turning Fannie and Freddie into cooperatives owned by mortgage lenders or remaking the firms as public utilities, subject to tight regulation and profit limits. Others wish to recreate them much as they used to be, private shareholder-owned institutions that serve a public mission ensuring the broad availability of mortgage credit.

Since they were thrown into the conservatorship of the FHFA in September, the White House has pushed the companies to help prop up mortgage markets and assist troubled homeowners. They were seized after mounting losses at the firms spawned fears they would collapse, deepening the global financial crisis.

The government has so far pumped $85 billion of capital into the companies to keep them solvent. That figure is likely to rise in the coming months, Lockhart told reporters last week, as mortgage defaults continue to mount at the companies. Both firms have seen high turnover in senior ranks, and executives have bristled at the government's involvement with the firms.

A high school friend of former President George W. Bush, Lockhart was a holdover from the Bush administration, where he also served in top posts in the Social Security Administration.

Lockhart helped establish FHFA as the new regulator for the mortgage giants after its predecessor, the Office of Federal Housing Enterprise Oversight, was phased out by a 2008 housing law that aimed to tighten oversight of Fannie and Freddie. But several weeks after the new agency was created, the officials determined the companies couldn't weather the growing storm in the U.S. housing market.

Lockhart was with Federal Reserve Chairman Ben Bernanke and Treasury Secretary Henry Paulson at FHFA's Washington offices to deliver the news of the conservatorship to former Fannie CEO Daniel Mudd and Freddie CEO Richard Syron. The decision cost both executives their jobs.

Just a few weeks after Lockhart took over as the regulator for Fannie Mae and Freddie Mac, his agency issued a blistering report on Fannie that cited major financial irregularities. The government fined the company $400 million.

Lockhart long echoed warnings from the Bush administration that the oversight of Fannie Mae and Freddie Mac wasn't sufficient. But Congress struggled to reach a consensus about what supervision of the companies should look like until last year after urgent warnings from then-Treasury Secretary Paulson.

While the director of the agency will have a fixed term in the future, the term for Lockhart, the first director, didn't have a fixed end date.

Lockhart said he has no job lined up, but that he hopes to return to work in the financial services industry in New York. He said he looked forward to "continue to work in a place where I can help us get out of these financial problems."

-Jessica Holzer, Dow Jones Newswires; 202-862-9228; jessica.holzer@dowjones.com; and Damian Paletta, The Wall Street Journal; damian.paletta@wsj.com