“Green” jobs accounted for 2.4 percent of the nation’s total employment in 2010, the Labor Department reported Thursday in its first-ever survey of green goods and services jobs.

According to the report, which gave a snapshot of the role that environmental consciousness plays in the U.S. economy, the United States had 3.1 million green jobs in 2010, the vast majority of them in the private sector. The public sector listed 860,000 green jobs, the report said.

In the past, employment in this field has been hard to measure because there’s been no consensus on what constitutes a green job. For its assessment, the Labor Department counted certain jobs in manufacturing, construction, utility and other sectors in which the primary function was to contribute to a green product or service. That includes the manufacture of hybrid vehicles, the production of solar power and construction projects such as weatherization.

It did not include, for example, jobs in grocery stores or restaurants that primarily sell organic food.

Jonathan Rothwell, a senior research analyst at the Brookings Institution, said there’s a distinction because these businesses “are not really adding value in a way that is unique to the green product.” Rothwell warned that the report should not be used as a barometer to measure the success of President Obama’s efforts to boost the number of green jobs. Because the report does not contain any growth figures, it does not reflect how the number of jobs may have changed over time. And even if such numbers were available, Rothwell said, it would be difficult to draw a direct cause and effect between policies and creation of such jobs.

Manufacturing accounted for the greatest number of green jobs among any private-sector industry, a promising sign for a strategically important sector, analysts said. Other sectors that accounted for large portions of the nation’s green jobs included construction (372,100 jobs) and professional, scientific and technical services (349,000 jobs).

There are “a lot of export opportunities for America if we can take leadership in this sector,” said Cai Steger, energy policy analyst with the National Resources Defense Council advocacy group.

The report also examined the picture at a state-by-state level. California had 340,000 green jobs in 2010 — more than in any other state and the District of Columbia — making up 2.3 percent of total employment.

The District, with 26,941 jobs in green goods and services, was near the top of the list of the proportion of jobs in relation to total employment, at 3.9 percent.