After decades of decline, the percentage of unionized workers nationwide increased in 2008, a UCLA study that was released Sunday has found.

Nationwide 12.6 percent of all workers are now in unions, a half percentage point increase versus the 2007 level, according to “The State of the Unions in 2008,” by the UCLA Institute for Research on Labor and Employment.

In Los Angeles, long a union stronghold, the percentage of unionized employees increased to 17 percent, up from 15.9 percent in 2007. Overall, L.A. had 1,227,600 union workers, almost half of all the union members in California, which itself has a far higher rate of unionization 17.8 percent in 2008 than other states. The state figure is up from 16.7 percent last year.

The study would appear to support the notion though it does not explicitly conclude that renewed efforts by unions to organize workers, especially in the health care, security and other service industries, have paid off. The Service Employees International Union, which has been highly active in Los Angeles, is one of the nation’s fastest growing unions.

However, the lead author of the study said that at least some of the uptick may be attributable to the slowdown in the economy, with layoffs hitting nonunionized workers harder than unionized workers.

“When there’s a big period of economic downturn as there is right now, that has a much bigger impact on unionization rates than what unions are doing,” said Ruth Milkman, the outgoing director of the UCLA Institute for Research on Labor and Employment and the study’s main author.

For instance, the state’s collapsing housing market has meant the number of largely nonunionized residential construction jobs have dropped precipitously. Meanwhile, jobs in the public sector and education, which are heavily unionized, tend to be better insulated from an economic skid, she said.

Indeed, the study found that Los Angeles’ high total unionization rate can largely be attributed to a very high public sector unionization rate of 57.6 percent. That compares with 37.2 percent nationwide.

It also found that contrary to popular perception, midlevel professionals and not blue-collar workers are more likely to be unionized in Los Angeles, California and the nation than any other group. High unionization rates in the public sector and educational services account for this finding.

Eric Christen, executive director of Coalition for Fair Employment in Construction, expressed skepticism that the numbers reflect unions gaining significant ground statewide.

“These numbers should always be placed in context and taken with a grain of salt,” said Christen, who had not seen the report.

His group is a statewide association of contractors and other businesses that seek to counter union influence in the construction industry.