The pressure to earn a bachelor’s degree draws young people away from occupational training, particularly occupations that do not require college, Mr. Sennett said, and he cited two other factors. Outsourcing interrupts employment before a skill is fully developed, and layoffs undermine dedication to a single occupation. “People are told they can’t get back to work unless they retrain for a new skill,” he said.

Image With 10 years of welding experience, Keelan Prados was able to pass an employers test and quickly begin a new job. Credit... Chris Becker for The New York Times

None of this deterred Keelan Prados from pursuing a career as a welder, one among roughly 200,000 across the nation. At 28, he has more than a decade of experience, beginning when he was a teenager, building and repairing oil field equipment in his father’s shop in Louisiana. Marriage to a Canadian brought the Pradoses to Maine, near her family. And before Mr. Prados joined Cianbro, an industrial contractor, he ran his own business, repairing logging equipment out of a welding and machine shop on the grounds of his home in Brewer.

The recession dried up that work, and last December, he answered one of Mr. McGrary’s ads. “I welded a couple of pieces of plate together for them and two pipes, and they were impressed,” Mr. Prados said. In less than two weeks, he was at work on Cianbro’s oil refinery project, earning $22 an hour and among the youngest of Mr. McGrary’s hires, most of whom are in their mid-30s to early 40s.

The Bureau of Labor Statistics does not track how often Mr. Prados’s experience  applying for a job and quickly being offered it  is repeated in America in the midst of huge and protracted unemployment. A bureau survey counts the number of job openings and the number of hires, but the data is not broken down by occupation.

The Conference Board, a business organization in New York, comes closer. In a monthly count of online job openings  listed on Monster.com and more than 1,200 similar Web sites  it breaks the advertised openings into 22 broad occupational categories and compares those with the number of unemployed whose last job, according to the bureau, was in each category. In only four of the categories  architecture and engineering, the physical sciences, computer and mathematical science, and health care  were the unemployed equal to or fewer than the listed job openings. There were, in sum, 1.09 million listed openings and only 582,700 unemployed people presumably available to fill them.

The Conference Board’s hard-to-fill openings include registered nurses, but the shortage is not as great as it was before the recession, particularly in battered states like Michigan and Ohio, said Cheryl Peterson, a director of the American Nurses Association.

“Until the downturn, it was easy for experienced registered nurses to find employment right in their communities, in whatever positions they wanted,” Ms. Peterson said. “Now it is a little more difficult because the number of job openings has fallen and we have more retired nurses, in need of income, coming back.”