WASHINGTON — A measure of Americans who signed contracts to buy homes increased last month to its highest level in two and a half years, the latest sign of improvement in the once-battered housing market.

The National Association of Realtors said Friday that its seasonally adjusted pending home sales index rose 1.7 percent in November from October to 106.4. That’s the highest since April 2010, when a home buyer tax credit caused an increase in sales. And after excluding those months when the tax credit was available, it’s the best reading since February 2007.