The National Association of Realtors said the index that keeps track of contracts of intention -- the legal space between paying a down payment and closing on a house -- fell 2.6 percent in the month after reaching the highest level in more than two years in July.
However, the index has shown year-over-year improvements for 16 consecutive months. In step with that data, the index in August is 10.7 percent higher than the 89.6 posting from August 2011.
"The performance in month-to-month contract signings has been uneven with ongoing shortages of lower priced inventory in much of the country, and across most price ranges in the West, but activity has remained at notably higher levels this year," said Lawrence Yun, NAR's chief economist in a statement.
The NAR said the pending home sales index rose 0.9 percent in the Northeast to 78.2.
The index fell 2.6 percent in the Midwest to 95. In the South it slipped 1.1 percent to 110.4. In the West, the index dropped 7.2 percent to 102.5.
NAR forecast existing home sales to climb percent in 2012 to 4.64 million homes and increase another 8 percent in 2013 to nearly 5.02 million.