WASHINGTON - Fewer people purchased previously occupied homes in April, a troubling sign that the weak housing market remains a drag on the economy.

Sales fell 0.8 percent in April to a seasonally adjusted annual rate of 5.05 million units, the National Association of Realtors said yesterday. That's far below the 6 million homes a year that economists say represents a healthy market.

Purchases made by first-time homebuyers did increase but not nearly enough to signal a housing recovery is on the way. First-time buyers are critical because they typically improve their properties and invest in their communities, a combination that helps home values rise.

Foreclosures, on the other hand, force prices down. They represented more than a third of all sales in April and more are expected in the months ahead.

Since the housing boom went bust, sales have fallen in four of the past five years and hit a 13-year low last year. Declining home prices and low mortgage rates haven't been enough to boost sales this year.

Some who want to buy can't, mostly because banks have tightened lending requirements and are insisting on larger down payments. Many buyers who can qualify for loans are holding off. They are worried that home prices have yet to bottom out.

Economists say it could be years before the housing market fully recovers.

A growing problem is that some sales that are under contract are falling apart. A separate survey from the trade group found that 11 percent of Realtors said a contract was canceled because an appraisal came in below the negotiated price. And 14 percent said a contract was renegotiated to a lower price because of a low appraisal.

The median sales price in April was $163,700. That's down 5 percent from the same month one year ago.

Sales of homes at risk of foreclosure fell in April. But they still made up 37 percent of all purchases. A record 1 million homes were lost to foreclosures last year and foreclosure tracker RealtyTrac Inc. expects 1.2 million more will be lost this year.