The National Association of Realtors said the index on contracts of intention -- the legal limbo between paying a down payment and closing on a house -- fell 1.4 percent May to June to 99.3.
May's index was also revised lower, to 100.7, the NAR said.
From June 2011, however, the index is up 9.5 percent, the trade group said.
Similarly, the Commerce Department said this week that sales of new single-family homes declined month-to-month in June, but rose 15.1 percent from June 2011.
Lawrence Yun, NAR's chief economist said, "Buyer interest remains strong, but fewer home listings means fewer contract signing opportunities."
"We've been seeing a steady decline in the level of housing inventory, which is most pronounced in the lower price ranges popular with first-time buyers and investors," he said.
The trend of a recent drop, but an annual gain, held true for three of four U.S. regions.
The NAR said the pending home sales index fell 7.6 percent in the Northeast, but is 12.2 percent higher than a year earlier. In the Midwest, the index fell 0.4 percent month-to-month, but remains 17.3 percent above 12 months earlier.
In the South, pending home contracts fell 2 percent, but are up 8.98 percent from June 2011.
The West is the exception. The pending home index rose in June, up 2.6 percent. That index is 3 percent higher than June 2011.