WASHINGTON — The National Restaurant Association’s Restaurant Performance Index stood at 99.5 in August, nearly unchanged from the previous three months.

The index was also below 100 for the fourth consecutive month, representing a contraction in the industry.

“Although the sales and traffic indicators remained soft in August, restaurant operators remain relatively optimistic that conditions will improve in the months ahead,” said Hudson Riehle, senior-vice president of the research and knowledge group of the N.R.A. “Restaurant operators’ outlook for sales growth improved somewhat in August, and their plans for capital spending activity held steady.”

The Current Situation Index, which measures trends such as same-store sales, traffic, labor and capital expenditures, was at 98.9 in August, up slightly from July but still below 100 for the 36th consecutive month.

Restaurant operators also reported a decline in same-store sales for the fifth consecutive month with 43% of operators reporting same-store sales declines in August. There was a continued net decline in customer traffic levels in August with 42% of operators reporting a traffic decline in August.

In addition, 38% of operators expect to have higher sales during the next six months while 17% expect to have their sales volume lower during the next six months. Restaurant operators are still not optimistic about the direction of the economy in general with 21% of operators said they expect economic conditions to worsen during the next six months.