ORLANDO, Fla. — The AFL-CIO formally endorsed President Barack Obama’s re-election bid Tuesday, saying it would mount a vast door-to-door effort for Democratic candidates in response to the money conservative groups are pouring into the campaign.

The labor federation said its strategy is to put emphasis on get-out-the-vote efforts.

AFL-CIO political director Mike Podhorzer said up to 400,000 union members will be staffing phone banks and knocking on doors to persuade voters to support federal, state and local candidates.

The strategy, announced at the AFL-CIO’s annual winter executive council meeting near Disney World, marks a shift from two years ago, when about two-thirds of organized labor’s political spending went directly to candidates and party campaign committees, Podhorzer said.

Unions hope to take advantage of a 2010 Supreme Court decision that allows union campaign workers to stop at the homes of any voter, not just those of union members, Podhorzer said. The same ruling allows corporations and unions to spend unlimited cash in support of, or against, candidates for elected office.

Union leaders have said they plan to spend more this election cycle than the $400 million they say they spent helping elect Obama and other Democrats in 2008.

Podhorzer wouldn’t say how much the AFL-CIO will spend this cycle. The federation, which represents 57 unions and about 12 million members, spent $53 million during the 2010 campaign cycle.

AFL-CIO President Richard Trumka said unions are more enthusiastic about Obama than they were a year ago, when Obama was mired in a debate with House Republicans over deficit reduction and didn’t seem focused on job creation.

“I think he’s made a complete pivot,” Trumka said of Obama.

Obama addressed the executive council Tuesday via conference call and thanked them for their support.

The federation is devoting most of its attention to six states: Florida, Michigan, Nevada, Ohio, Pennsylvania and Wisconsin.

It hopes to register at least 20 percent of an estimated 2.3 million union members who are not registered to vote.