The nation's labor unions saw another steep decline in membership last year, even as the economy showed signs of recovery and job losses slowed.

The Bureau of Labor Statistics reported Friday that unions lost 612,000 members in 2010, dropping the unionized share of the work force to 11.9 percent from 12.3 percent in 2009. That follows a loss of 771,000 workers in 2008, continuing a steady decline from the 1950s when more than a third of workers belonged to unions.

The news comes as union officials are pressing President Barack Obama and other leaders to invest more money in infrastructure projects like repairing highways and bridges to help stimulate the economy and create new jobs. That plea is meeting stiff resistance from Republicans intent on cutting spending sharply to pare back the rising national debt.

Union membership in the private sector fell from 7.2 percent to 6.9 percent, a low point not seen since the infancy of the labor movement in the 1930s. The steepest decline was seen in the construction industry, where unemployment remains around 20 percent.

Public employment unions saw a 1.2 percent decline, mostly from job cuts among state and local government workers. Those unions could see further declines this year, as states eliminate jobs in an effort to make up multibillion-dollar budget deficits.

"In the absence of federal support for state and local governments, public sector cutbacks will continue to depress the overall union membership rate," said Ben Zipperer, a senior research associate of the Center for Economic and Policy Research.

Kate Bronfenbrenner, director of labor education research at Cornell University's School of Industrial and Labor Relations, said unions could stem the decline if the economy continues to expand and jobs grow in areas where union density is strong, such as transportation and the service sector. She warned that unions need to spend more resources on organizing new workers, even as they try to pass legislation that would make it easier to form unions.

"In this economy, the unions can't stand still," Bronfenbrenner said. "They can't stop organizing while they are trying to get labor law reform."

But unions are now spending more money to fight efforts in GOP-led state legislatures that want to cut salaries, pensions and other benefits for public employees and could place more restrictions on the ability of public and private employees to unionize.

"In states across the country, workers are facing heightened efforts to undermine public workers and their unions," said AFL-CIO spokeswoman Alison Omens. "It's a real assault."

Last year was the first time that public employees made up a majority of all union workers. Unlike private employers, government offices do not hire outside consultants to help them fend off union organizers. But newly elected governors and lawmakers in Ohio, Wisconsin, Florida and other states are backing legislation that would make government offices less union-friendly.

In other highlights from the report:

_ Black workers were more likely to be union members than white, Asian or Hispanic workers.

_ Union membership was highest among 55- to 64-year old workers and lowest among those ages 16 to 24.

_ New York had the highest union membership rate at 24.2 percent and North Carolina had the lowest at 3.2 percent.