WASHINGTON — Sales of existing houses rose last month, surpassing expectations, as buyers snapped up deeply discounted properties in parts of the country hit hardest by the housing bust.

However, the number of unsold properties hit an all-time high, the latest indication that the worst housing slump in decades is far from over. Prices nationwide are not predicted to hit bottom until early next year.

The National Association of Realtors reported yesterday that sales rose 3.1 percent to a seasonally adjusted annual rate of 5 million units, up from June’s downwardly revised rate of 4.85 million units. Sales had been predicted to rise by only 1.6 percent, according to economists surveyed by Thomson/IFR.

“The process of a recovery has begun,” said Joel Naroff, president of Naroff Economic Advisors. “It’s not going to be short and swift, but it’s begun nonetheless.”

But sales were about 13 percent lower than a year ago and prices were down dramatically. The median price for a house sold in July dropped to $212,000, down by 7.1 percent from a year ago.

And despite the third monthly sales increase this year, the number of unsold single-family homes and condominiums rose to 4.67 million, the highest number since 1968, when the Realtors group started tracking the data.

That represented an 11.2-month supply at the July sales pace, matching the all-time high set in April.

Until the inventory level is reduced to more normal levels, analysts say, the housing slump is likely to persist. The inventory level is being driven higher by a massive wave of mortgage foreclosures.

Between 33 percent and 40 percent of sales activity is coming from foreclosures or other distressed properties, estimated Lawrence Yun, chief economist at the Realtors group.

While buyers are pouncing on lower prices — especially in places such as California, Florida and Nevada — sales are sluggish in formerly stable states such as Texas.

“People are responding to lower prices,” Yun said, but there is “too much uncertainty” about the housing market’s future to mark a definite bottom.

In Las Vegas, sales were up 96 percent last month, after prices fell more than 25 percent to a median of $220,000, according to The Associated Press-Re/Max Monthly Housing Report, which analyzed house sales recorded by all real estate agents in 55 cities, regardless of company affiliation.

Sales in Los Angeles jumped 31 percent after prices fell 35 percent over the past year to a median of $335,000, according to the AP-Re/Max report.

In Miami, sales were up 9 percent while prices dropped nearly 10 percent to a median of $280,000. One of those sellers last month was Jennifer Del Pino, who unloaded her 3,600 square-foot Miami home to a buyer from Germany for $490,000.

She cut her asking price by $60,000, but sold her house in about a month.

“It’s kind of a relief for me,” she said.

Home sales tumbled in most big Northeastern cities last month — with only Passaic, N.J., showing a healthy jump in activity.

Sales of existing houses in the region declined nearly 12 percent in July from a year ago, the National Association of Realtors said. The median price in the Northeast was $278,700, down almost 5 percent from July 2007.

In the one bright spot, Passaic, sales jumped 38 percent over July last year. But the rapid sales pace could be stymied by glut of properties coming onto the market. The supply of unsold homes grew 32 percent to 10.6 months, and the median price slid 6 percent to $400,000.

In contrast, Pittsburgh posted the worst sales decline at 31 percent from July 2007. But prices offered a sliver of hope, dipping less than 1 percent to $132,000, the smallest drop in the region.

Foreclosures are leaving their mark in Providence. Nearly one of five sales in the area were distressed sales, said Ron Phipps of Phipps Realty in Warwick. The discounted properties are weighing down the market, where the median price fell by 13 percent last month to $234,900, the AP-Re/Max report showed. Sales there also slipped 9 percent in July.

“A lot of sellers are nostalgic for what was, so they’re disengaging from the market,” Phipps said. The supply of unsold homes shrank nearly 3 percent in July as a result.

In Boston, the supply of homes for sale declined markedly, signaling a possible turnaround in the offing. Judy Moore, a local agent with Re/Max Landmark, said the condo market already is showing signs of life.

Overall, Boston home sales fell 12 percent in July and the median price decreased 8 percent to $355,000, according to the AP-Re/Max report. While Moore expects August sales and prices to decline year-over-year, she thinks the drop in both will be less severe than July’s.

“It’s been fits and starts, but there’s always some activity going on,” Moore said.