That ominous shadow inventory of repossessed and soon-to-be repossessed homes is getting smaller.

Standard and Poor’s (S&P) has released its third-quarter shadow inventory update, which shows both the volume of distressed assets and the amount of time it’d take to liquidate these properties is contracting.

S&P says the volume of distressed residential mortgages included in its shadow inventory estimate remained “extremely high” at $384 billion in the third quarter, but it has declined in each quarter since mid-2010. S&P’s third-quarter evaluation is down from $405 billion at the end of the previous quarter.

“We believe this points to a continued drop in the amount of time it will take to clear this ‘shadow inventory’ over the next year assuming national liquidation rates do not decline abruptly,” the analysts at S&P said in their report.

Regional default and liquidation rates varied widely in the third quarter of 2011, but overall improvements prompted S&P to lower its projection of the number of months to clear the supply of distressed homes on the market and coming down the pipeline.

The agency now estimates that it will take 45 months to work through the national shadow inventory. This assessment is seven months below S&P’s peak estimate of 52 months in March 2011, but is three months longer than the agency’s estimate a year ago.

S&P calculates shadow inventory as the number of properties for which borrowers are 90 days or more delinquent on their mortgage payments, properties in foreclosure, and properties that are REO. The agency also includes 70 percent of the loans that “cured” from being 90 days delinquent within the past 12 months because these loans carry a higher risk of redefault.

S&P’s analysis of the shadow inventory uses only non-agency (non-GSE) data, but the company’s analysts say they believe the months-to-clear is similarly high for the market as a whole.