Home prices nationally bumped up 0.9 percent in April compared to March, according to new data released by Integrated Asset Services, LLC (IAS) Tuesday.

That follows a 1.1 percent month-to-month gain recorded by the Denver-based valuation company in March, which represented the first time in eight months that IAS’ home price benchmark inched into positive territory.

But even with the monthly increases, the IAS360 House Price Index is down 2.8 percent from April 2009, demonstrating just how sluggish a full recovery will be.

With April’s gain, IAS says home prices nationally are 23.9 percent below the peak hit in July of 2007.

Three of the four U.S. census regions registered respectable gains for the month of April, with the Midwest adding 1.9 percent to home values; the South, primarily on strength along its central corridor, 1.8 percent; and the West 1.1 percent. Only the Northeast, with a 0.7 percent decline – the region’s eighth in a row – lost ground for the month.

“Arguably, the housing market is in better shape today than it was a year ago, but it’s reasonable to think federal

tax credits have propped up home sales and prices to some degree,” said Dave McCarthy, president and CEO of Integrated Asset Services. “I’m concerned the end of government support could lead to renewed weakening in the market.”

Homebuyers who close on a deal by June 30 are eligible for the administration’s credit worth up to $8,000 for first-time buyers and $6,500 for existing homeowners. The deadline for signing contracts was the end of April. Many analysts believe demand may cool after the effect of the tax credit fades, which would put added pressure on the housing marketplace.

Also weighing on the near-term outlook is an estimated stockpile of more than 4 million unsold homes on the market, the highest number since July according to data from the National Association of Realtors (NAR).

Beyond that looms the so-called “shadow inventory” of homes that are in the process of foreclosure or are already seriously delinquent and will be soon heading down that pipeline toward REO status. Industry estimates vary as to pinpointing the exact number of properties lurking in the shadows – anywhere from 1 million to more than 7 million.

The latest report from Lender Processing Services (LPS), whose numbers are based on the company’s extensive national loan-level database, puts the total volume of non-current U.S. home loans – including those that are delinquent, in foreclosure, and REO – at just over 7.3 million.

McCarthy says he can’t discount the fact that the IAS360 index of home prices has turned positive after such a long stretch of down months, but “given all that’s in front of us, we can’t forget this improvement may be fleeting as well,” he said.