Borrowing costs are at historic lows. The average U.S. rate for a 30-year fixed mortgage was 4.69% last year, the lowest in annual data going back to 1972, according to mortgage financier Freddie Mac, based in McLean, Va. The rate in March was 4.84%, the company said.

By 2012's fourth quarter, the average fixed rate may rise to 6%, according to the Mortgage Bankers Association.

"If you can jump through the hoops to get a mortgage, and there will be hoops, then this is an amazing time to purchase real estate," said Robert Stein, a senior economist at First Trust Portfolios LP in Wheaton, Illinois, and the former head of the Treasury Department's Office of Economic Policy. "There are going to be a lot of people kicking themselves a few years from now because they didn't take advantage of the low prices and the low mortgage rates."

Tighter Lending

Cheap financing hasn't done enough to boost home sales in part because lenders are being more selective with applicants, according to Federal Reserve Chairman Ben Bernanke. Fed policy makers have described the housing market as "depressed" in statements following their last eight meetings.

"Although mortgage rates are low and house prices have reached more affordable levels, many potential homebuyers are still finding mortgages difficult to obtain and remain concerned about possible further declines in home values," Bernanke said in Congressional testimony last month.

The share of banks reporting tighter mortgage standards in the first quarter rose to 16%, the highest since 1991, according to the Fed's Senior Loan Officer Survey.

Federal regulators are proposing rules that may make lending even more stringent, including a requirement that banks and bond issuers keep a stake in home loans they securitize if the mortgage borrowers have imperfect credit and down payments of less than 20%. Borrowers who don't meet the criteria would pay higher rates to compensate lenders for risk.

Fannie Phase-Out

As mortgage requirements rise, rates could follow as Congress and the Obama administration consider phasing out government-controlled Fannie Mae and Freddie Mac. The companies hold federal charters mandating they increase the availability of mortgages through securitization. In Fannie Mae's case, that order goes back to the Great Depression, when it was created as part of President Franklin D. Roosevelt's New Deal.