WASHINGTON — A now-expired homebuyer tax credit and low mortgage rates helped boost sales of previously occupied homes in April. The improvements aren't likely to last.

The tax credit is now gone. And economists caution that Americans are facing so many financial obstacles that falling rates alone won't be enough to lift the housing market.

"Although mortgage rates have fallen sharply, the combination of high unemployment, heavy indebtedness and tight credit suggest to us that demand will stumble," said Paul Dales, an economist at Capital Economics.

Sales of previously owned homes rose 7.6 percent to a seasonally adjusted annual rate of 5.77 million, the National Association of Realtors said Monday.

The sales increase sparked a rise in home prices. The median price for a new home rose to $173,100, up 4 percent from a year ago.

Mortgage rates fell last week to the lowest level for the year. The average rate on a 30-year loan ticked up slightly to 4.87 on Monday, according to financial publisher HSH Associates. That was just above the record low of 4.83 percent last December,