National home prices fell 0.3 percent in November, the Denver-based default and valuation firm Integrated Asset Services, LLC (IAS) said Tuesday.

The monthly decline is the third straight in the IAS360 House Price Index, and puts the company’s benchmark for U.S. housing at essentially the same level as at the beginning of 2009.

“Given the weak labor market and the tight credit environment, it’s not surprising to see some weakening in prices through these winter months,” said Dave McCarthy, president and CEO of Integrated Asset Services. “Even in the best of economies, the winter season is associated with a reduced number of home sales and an increase in marketing times. And these are hardly the best of economies.”

McCarthy says he’s particularly concerned about the nation’s high unemployment rate that’s causing more homeowners to fall behind on their mortgage payments.

Recent reports suggest the number of distressed properties in the foreclosure pipeline is both substantial and growing, and McCarthy warns that the resulting “shadow inventory” of REO that banks and mortgage companies are likely to place on the market could weigh on house prices well into 2010.

The South, for its part, saw home prices jump a solid 2.3 percent for November as the steady declines in Florida slowed, IAS reported. In Florida, values slipped only fractionally again for the month, but after dropping nearly 45 percent from their high-water mark in June 2006, IAS says the worst declines may be over for the hard-hit market.

The warm-up in the Sunshine State and its Southern counterparts, though, wasn’t enough to lift the IAS360 HPI into positive territory.

The Northeast fell for the third month in a row, losing another 1.8 percent from October to November, as important population centers like Westchester County, New York; Morris County, New Jersey; and Frederick County, Maryland suffered declines upwards of 5 percent.

The Midwest, too, lost more ground for the month, slipping another 1.7 percent, while the West gained 0.5 percent for the second month in a row.

Mortgage rates, in the meantime, have begun to inch up, putting even more pressure on homebuyers. At the end of 2009, Freddie Mac reported that the average 30-year fixed-rate mortgage was 5.05 percent, the first time the mortgage benchmark has been above 5 percent threshold since October.

“Despite the extent of the [price] declines to date, the risk of renewed weakening in house price still looms large,” McCarthy said, with an even greater potential for another wave of distressed properties hitting the market from both private sellers and banks.