Shaking off a spring and early summer softening, U.S. retail sales in August showed a 0.4% gain, the largest increase since March.

The U.S. Commerce Dept. report showed that excluding auto sales, retail sales grew 0.6% for the month compared to the month prior. That differential shows just how weak the auto industry continues to be in the U.S.

The increase in sales activity came after a harsh decline in May and flat sales activity in June and July, the Commerce Dept. said.

Retail sales rose a revised 0.3% in July, the government said, after declines in May and June, a downward shift that alarmed economists about America’s economic recovery.

Still, even with improved sales results in July and August, most economists are calling for only 2% retail growth for the second half of 2010. “Jobs are not readily available, wages are stagnant and income growth is mediocre,” said Joel Naroff, chief economist at Naroff Economic Advisors.

Weak auto sales are also a point of concern. August auto sales fell 0.7% from July, making August the auto industry’s worst sales month since 1983.