The inventory of existing homes for sale rose 1.5 percent to 3.55 million in March. (Jim R. Bounds/BLOOMBERG)

Sales of previously owned homes rose slightly in March after plunging in February, but the housing market still shows no real momentum, even though interest rates and home prices remain relatively low.

Existing home sales rose 3.5 percent to a seasonally adjusted rate of 5.1 million in March from February, the National Association of Realtors reported Wednesday.

Many economists gave two reasons for the boost in sales: investors buying foreclosed homes at cheap prices, and cash-strapped borrowers accelerating their purchases before a scheduled increase in fees for mortgages backed by the Federal Housing Administration.

But last month’s purchase sales were down 6.3 percent compared with a year earlier, when a federal tax credit for home buyers temporarily invigorated the housing market.

“There’s still nothing out there that’s a driving force for the housing market,” said Mike Larson, an analyst with Weiss Research. “Psychologically and financially, people are not able or eager to buy homes.”

Joblessness, economic uncertainty and tight lending standards continue to dampen demand for housing, even though homes are at their most affordable level since the National Association of Realtors launched its affordability index in 1970. Economists say the housing market’s recovery continues to lag behind that of the wider economy.

The Realtors group reported that the national median price of an existing home fell to $159,600, a 5.9 percent drop from March 2010. Several economists predict that prices will continue to decline at least through the first half of this year.

One of the main reasons for soft prices is the prevalence of foreclosures and other distressed properties, which are sold at steep discounts and made up 40 percent of the market last month — the highest share since April 2009, according to a separate survey by the Realtors.

Given the excess supply of foreclosures, “it’s hard to argue that prices will not fall throughout this year, perhaps by around 5 percent,” Paul Dales, a senior economist at Capital Economics, wrote in a note to clients.

The inventory of homes for sale rose 1 percent to 3.55 million last month. If sales continued at the same pace, it would take 8.4 months to clear the for-sale homes off the market, the Realtors said. A more healthy supply would be in the five- to six-month range.

But there are glimmers of hope for the pivotal spring selling season.

The Mortgage Bankers Association reported Wednesday that applications for mortgages to buy homes increased 10 percent last week from a week earlier to the highest level since Dec. 3, according to the group’s purchase index.

“This pickup in demand should show up in improved existing home sales in April and May, unless lending conditions tighten,” said Patrick Newport, an economist at IHS Global Insight.