WASHINGTON — Improved sales and traffic levels in October boosted the National Restaurant Association’s Restaurant Performance Index to its highest levels in more than three years as it stood at 100.7 for the month.

“October’s R.P.I. gain was driven by continued improvements in the same-store sales and customer traffic indicators,” said Hudson Riehle, senior vice-president of the research and knowledge group for the association. “Most notably, a majority of restaurant operators reported higher same-store sales in October, the first such occurrence since August 2007.”

The R.P.I. was up 0.4% from September and was at the strongest level since September 2007. It was also above 100 for the second consecutive month, indicating industry expansion.

“In addition to improving current situation indicators, restaurant operators are increasingly optimistic about sales growth in the coming months and also reported a positive outlook for staffing levels for the first time in six months,” Mr. Riehle said.

More than 50% of restaurant operators reported a same-store sales gain between October 2009 and October 2010, up from 44% of operators in September and the first time since August 2007 when a majority of operators reported higher same-store sales.