Uncle Sam's interventions in the housing market have pushed home prices 5% higher on a national average than they would have been otherwise, Goldman Sachs estimates in a report released late Friday.

The government over the past year has slowed the pace of foreclosures through moratoria and the drive to modify mortgage terms to keep more borrowers in their homes. It also has pumped up demand for housing by giving tax credits to many first-time home buyers and by driving down mortgage interest rates. As a result, home prices in some areas have risen in recent months, particularly for homes that appeal to investors and first-time buyers. Bidding wars for the more attractive bank-owned homes have become common.

But these artificial props won't last forever and may have created a false bottom in the market. "The risk of renewed home-price declines remains significant," Goldman economist Alec Phillips writes in the report, "and our working assumption is a further 5% to 10% decline by mid-2010."

Federal government policies encouraging loan mods have reduced the supply of homes on the market temporarily because it takes months for loan servicers (the firms that collect mortgage payments) to figure out which borrowers qualify. Some states have added their own restrictions on foreclosures that drag out the process further. In many cases, borrowers who get loan mods will default again within a year or so, meaning the problem has been delayed rather than solved. That means there is a large but impossible-to-measure "shadow" inventory of homes that eventually will hit the market.

Goldman estimates the tax credit has boosted sales by 200,000 units. Congress is debating whether to extend that credit beyond Nov. 30. Goldman says it "appears likely to be extended for at least a few months but probably no longer than through the first half of 2010."