by Steven Greeenhouse

For the first time in American history, a majority of union members are government workers rather than private-sector employees, the Bureau of Labor Statistics announced on Friday.

In its annual report on union membership, the bureau undercut the longstanding notion that union members are overwhelmingly blue-collar factory workers. It found that membership fell so fast in the private sector in 2009 that the 7.9 million unionized public-sector workers easily outnumbered those in the private sector, where labor’s ranks shrank to 7.4 million, from 8.2 million in 2008.

“There has been steady growth among union members in the public sector, but I’m a little bit shocked to see that the lines have actually crossed,” said Randel K. Johnson, senior vice president for labor at the United States Chamber of Commerce.

According to the labor bureau, 7.2 percent of private-sector workers were union members last year, down from 7.6 percent the previous year. That, labor historians said, was the lowest percentage of private-sector workers in unions since 1900.

Among government workers, union membership grew to 37.4 percent last year, from 36.8 percent in 2008.

Gerald W. McEntee, president of the American Federation of State, County and Municipal Employees, voiced dismay that government employees now represented a majority of union members.

“It’s a very bad sign,” he said. “We’ve been banged around some, but when you see what’s been happening to the industrial base of this country, to the steelworkers, to the autoworkers, they’re been hammered much more.”

After rising the two previous years, overall union membership fell by 771,000 in 2009, to 15.3 million, largely because employment declined over all. But the rate of private-sector unionization fell because two sectors where unions are especially strong — manufacturing and construction — suffered especially large job losses. Construction lost more than 900,000 jobs last year, falling to 5.9 million, while 1.3 million factory jobs were lost, declining to 11.6 million.

The overall unionization rate edged lower, to 12.3 percent last year from 12.4 percent in 2008.

Damon A. Silvers, the A.F.L.-C.I.O.’s policy director, said the decline in private-sector unionization “tells us that good jobs are disappearing faster than bad jobs.”

According to the labor bureau, median weekly earnings for full-time unionized workers were $908 last year, compared with $710 for workers not represented by unions. The bureau attributed this difference not just to unionization but also to variations by occupation, industry and company size.

Notwithstanding the recession, government employment grew last year, inching up 16,000, to 22,516,000, according to the bureau.

Fred Siegel, a visiting professor of history at St. Francis College in Brooklyn and a senior fellow at the Manhattan Institute, a conservative research organization, said, “There were enormous political ramifications” to the fact that public-sector workers are now the majority in organized labor.

“At the same time the country is being squeezed, public-sector unions are a rising political force in the Democratic Party,” he said. “They depend on extra money for the public sector, and that puts the Democrats in a difficult position. In four big states — New York, New Jersey, Illinois and California — the public-sector unions have largely been untouched by the economic downturn. In those states, you have an impeding clash between the public-sector unions and the public at large.”

Several labor officials and scholars said private-sector workers could regain their majority in a year or two because of potential large-scale layoffs of government workers in the face of the budget squeeze faced by so many cities and states.

Assessing the drop in private-sector unionization, Paula B. Voos, a labor relations professor at Rutgers, said, “It’s a sad commentary on the ability of private-sector workers to unionize.”

“Unions have less strength when they represent a lower percentage of workers,” she said. “Nonetheless, unions have strength in those sectors of the economy where they are organized. Workers who are in the entertainment industry, workers who are on the docks of the Port of New York and New Jersey still have the strength of their labor organizations.”

Noting that union members generally have higher earnings, Labor Secretary Hilda Solis said in a statement: “As workers across the country have seen their real and nominal wages decline as a result of the recession, these numbers show a need for Congress to pass legislation to level the playing field to enable more American workers to access the benefits of union membership. This report makes clear why the administration supports the Employee Free Choice Act,” a bill that would make it easier to unionize.”

But J. Justin Wilson, managing director of the Center for Union Facts, a corporate-backed group opposing that legislation, had a different response to the report.

“Labor union membership is an outdated concept for most working Americans,” he said. “It is a relic of Depression-era labor-management relations.”