Prices on homes backed by Fannnie Mae and Freddie Mac slid 0.5% from June to July, and the previously reported June decline of 0.3% was downwardly revised to a far more signifcant 1.2% drop, the Federal Housing Finance Agency reported Wednesday.

FHFA said the unusually large revision mainly reflects the addition of new data from late June that show considerably weaker prices than earlier in the month.

For the 12 months ending in July, prices on lower-end homes fell 3.3%, putting the FHFA's Home Price Index 13.8% below its April 2007 peak, a new low for the housing recession. The July 2010 index of 192.4 is roughly equal to what it was in September, 2004.

Across the nine Census regions, June-to-July prices rose 1.1% in the Pacific, lost 1.5% in the Mountain, dropped 1% in the West North Central, fell 0.7% in the West South Central, declined 0.8% in the East North Central, rose 0.3% in the East South Central, fell 0.1% in New England, rose 0.2% in the Middle Atlantic and lost 1.6% in the South Atlantic.

Year-over-year, all regions were down, with the Pacific -1.8%, Mountain -7.3%, West North Central -1.9%, West South Central -0.5%, East North Central -4.4%, East South Central -1.9%, New England -1.4%, Middle Atlantic -0.3% and South Atlantic -7.2%.