The worst days of the housing slump may lie ahead.

Buyers vanished from the housing market in March, as sales of new homes plummeted to the lowest level since the housing recession of the 1990s, the government said on Thursday.

Builders are now faced with the biggest backlog of unsold homes in more than a quarter century, a sign that home values may continue to drop.

“People are obviously reluctant to buy so long as prices continue to fall,” said Bernard Baumohl, managing director of the Economic Outlook Group in Princeton, N.J. “They have no desire to buy a house that is going to be worth less two months later.”

Even those who wish to buy may be stymied, Mr. Baumohl said, as banks and mortgage lenders tighten their credit standards amid broader troubles in the economy.