WASHINGTON (MarketWatch) -- U.S. home prices fell at a record rate in June, putting more pressure on an already-fragile financial system.

The Case-Shiller index of 20 major metropolitan areas for the month dropped 15.9% from June 2007, Standard & Poor's reported Tuesday.

The Case-Shiller index, which tracks multiple sales of the same homes, is considered by many observers to be the best gauge of national and metro-level real-estate values. While only slightly worse than the 15.8% decrease seen in the previous month, June's drop represents a new record decline.

Prices tracked in a separate index of 10 cities fell a record 17.0% in the past year.

"While there is no national turnaround in residential real-estate prices, it is possible that we are seeing some regions struggling to come back, which has resulted in some moderation in price declines at the national level," said David Blitzer, chairman of the Index Committee at Standard & Poor's. "Nevertheless, not one market is showing a positive return over the past 12 months and seven of the metro areas are reporting declines in excess of 20%."

Falling house prices make it more difficult for owners to tap their home equity or refinance their mortgages. Economists are also worried about credit-card and other debt.

Later Tuesday, the Office of Federal Housing Enterprise Oversight will report its national home price index. The OFHEO index showed prices were down 1.7% in the first quarter.

As with Case-Shiller, the OFHEO index tracks multiple sales of the same homes. However, OFHEO doesn't include homes with nonconforming mortgages, such as those with jumbo mortgages for more than $417,000.

©1997-2002 MarketWatch.com, Inc. All rights reserved. See details at http://custom.marketwatch.com/custom/docs/useragreement.asp.

Copyright 2008 MarketWatch.com Inc. All Rights Reserved