A federal regulator on Wednesday urged more than 800 thrift institutions to suspend all foreclosures while the Obama administration develops plans to keep borrowers in their homes.

John Reich, director of the Office of Thrift Supervision, said that by doing so, thrifts "would be supporting the national imperative to combat the economic crisis." But cooperation with the request is voluntary.

The Obama administration plans to spend $50 billion to combat foreclosures of owner-occupied middle-class homes, but is divulging few details. An announcement of the administration's housing plans is expected in the coming weeks.

"We're urging them to do it, but we're not going to try to force anyone to comply," said William Ruberry, a spokesman for the thrift agency. "We thought it was reasonable -- because the details (of the government's plans) are expected to be imminent."

Thrifts differ from banks in that, by law, they must have at least 65 percent of their lending in mortgages and other consumer loans -- making them particularly vulnerable to the housing downturn.

Some of the largest thrifts have collapsed over the past year. The failure of Seattle-based Washington Mutual Inc. in September was the largest bank collapse in U.S. history. IndyMac Bank, a Pasadena, Calif.-based thrift, failed last July in a prelude to the broader financial crisis that erupted in September.

The institutions regulated by the Office of Thrift Supervision range in size from small community banks to big institutions like ING Bank, part of Dutch financial giant ING Groep NV.

Thrifts are being closely examined by federal inspectors for signs of heavy exposure to declining markets, or troubled areas such as construction and real estate loans.

Twenty-five U.S. banks failed last year, far more than the previous five years combined, and nine banks have failed so far this year. It's expected that many more banks won't survive this year amid the pressures of tumbling home prices, rising mortgage foreclosures and tighter credit. Some may have to merge with other institutions.