WASHINGTON (Reuters) - Contracts to buy U.S. previously owned homes rebounded sharply in June as an improvement in supply and some moderation in mortgage rates pulled buyers in from the sidelines.

The National Association of Realtors (NAR) said on Wednesday its Pending Home Sales Index, based on signed contracts, surged 4.8% last month to 74.3. Pending home sales rose in all four regions last month.

Economists polled by Reuters had forecast contracts, which become sales after a month or two, rebounding 1.5%. Pending home sales dropped 2.6% in June on a year-on-year basis.

"The rise in housing inventory is beginning to lead to more contract signings," said NAR Chief Economist Lawrence Yun.

Mortgage rates have pulled back after surging in the spring and house price increases are slowing. But a sharp rebound in home sales in unlikely.

A Conference Board survey on Tuesday showed the share of consumers planning to buy a house over the next six months slumped in July to the lowest level since February 2013.

The Federal Housing Finance Agency reported on Tuesday that houses prices increased 5.7% year-on-year in May, the smallest gain in 10 months after rising 6.5% in April.