Home prices fell at a slower rate in July, continuing a six month trend earlier in 2009, but concerns about longer term stability remain, according to the latest report of the S&P Case Schiller Home Price Indices.

The results show that “although still negative, the annual rate of decline of the 10-City and 20-City Composites improved compared to last month’s reading.”

The 10-City and 20 City composite Home prices indices declined 12.8 pct and 13.3 pct respectively.

The report also found thirteen of the metropolitan statistical areas (MSA) had at least three months of “positive prints,” said David M. Blitzer, Chairman of the Index Committee at Standard & Poor’s.

Blitzer indicated some wariness, however.

“These figures continue to support an indication of stabilization in national real estate values, but we do need to be cautious in coming months to assess whether the housing market will weather the expiration of the Federal First-Time Buyer’s Tax Credit in November, anticipated higher unemployment rates and a possible increase in foreclosures.”