"In contrast to the broad gains in most construction segments, employment in public works construction has been flat or falling," Simonson says.

These counts, which lag the overall industry totals by one month, show a drop of 3,500 employees (1.5 percent) in highway, street, and bridge construction from February 2012 to February 2013 and a pickup of only 1,000 (0.7 percent) employees in water and sewer system construction.

At the other extreme, Simonson says, oil and gas pipeline construction employment soared by 16,300 (14.5 percent), and power and communication system construction employment jumped by 14,400 (13.0 percent).

Association officials say that these diverging employment patterns mean it's essential for the industry to be able to recruit workers from abroad if necessary to fill gaps in critical segments. It is equally important that the public sector stop underinvesting in vital highway and water infrastructure, they contend.

"Construction is now adding jobs at a faster clip than the economy as a whole, but there are twin threats to both the industry and overall economic expansion," says Stephen E. Sandherr, the association's CEO. "To keep the economy on track, the nation needs up-to-date infrastructure that can deliver energy, goods, and people. Policymakers need to do their part by investing in public infrastructure and by allowing construction to import workers when needed."