The number of properties for rent in Spain climbed 55 percent in the past two years to 3.3 million, the highest since the Ministry of Housing started collecting the data in 2004. Rents in cities, including Madrid and Barcelona, are falling for the first time in seven years with declines of as much as 8 percent, according to Madrid-based property research firm Idealista.com.

“Those who need to sell but can’t are being forced to lease,” said Fernando Encinar, co-founder and head of research at Idealista.com, Spain’s largest real estate Web site with 308,000 listings for rent and purchase. “We haven’t seen this number of properties for rent since the 1950s.”

Spain built about 29 percent of new homes in the European Union from 2001 to 2007, even as it represented just 9 percent of the population. The resulting glut of 1.5 million unsold houses and apartments sparked the end of a decade-long real estate and construction boom that accounted for about 20 percent of the country’s gross domestic product in 2007.

The ensuing housing slump has tipped the economy into the worst recession in 60 years with the unemployment rate climbing to 19 percent, the highest in the EU. Home sales fell by more than a third in the 12 months through May, the latest government data show.

Joblessness in Spain may reach 20.5 percent by the end of 2010, according to estimates from the European Commission.

“Redundancy is having a huge impact on home sales, hence many people are turning to renting,” said Ben May, an economist at Capital Economics Ltd. in London. “Even people who still have jobs are clearly going to be worried and those that are in a position to buy are waiting for prices to fall.”