Hartford — The leading Democratic candidates for governor are trading union endorsements in the run-up to next week's party convention.

Greenwich businessman Ned Lamont, the party's 2006 U.S. Senate candidate, announced the endorsement Wednesday of the Connecticut Laborers' District Council, representing roughly 7,500 workers in the state.

Former Stamford Mayor Dan Malloy, Lamont's chief rival for the nomination, announced his backing by the largest health care and building services workers unions in the state, SEIU Healthcare Local 1199, and SEIU 32BJ. The unions represent 20,000 and 4,500 workers in the state, respectively, the Malloy campaign said.

The battle for labor comes as the Democratic field prepares for a thinning out after the convention.

Malloy won the party endorsement in a convention upset four years ago, working delegates on the floor to eke out a victory over the eventual party nominee, New Haven Mayor John DeStefano Jr.

At that same convention, Lamont lost to Sen. Joe Lieberman, whom he would go on to defeat in the Democratic primary, then lose to in the 2006 general election.

Malloy has also been endorsed by Communications Workers of America Local 1298, Operating Engineers Local 478, Carpenters Local 210, the Connecticut Police and Fire Union, and local police unions in New London, Hartford and Waterbury.

Lamont has been endorsed by Roofers Local 12, Sheet Metal Workers Local 40, United Food and Commercial Workers Local 371, Bricklayers and Craftworkers Local 1, and Iron Workers Local 424.

In a brief interview, Malloy said he thought his most recent endorsements would help in the anticipated August primary, when organized labor can help mobilize supporters and get voters to the polls.

"The world has changed a lot in four years," Malloy said, "and I believe that these unions are looking for someone that they trust to lead Connecticut out of this crisis."

In a news release announcing the Laborers' Council endorsement, Lamont struck a similar tone.

"I share their dedication to workers' rights, and as governor, my priority will be to create good-paying jobs with reliable benefits for all the working families in our state," Lamont said.

t.mann@theday.com