CHICAGO, July 25 - The huge split in organized labor has been fueled by stagnant living standards for many workers, by the ascendancy of the service sector and by labor's lack of success in politics and unionizing workers. But as much as anything, the schism reflects the conflicting ambitions of two titans of labor, John J. Sweeney, the president of the A.F.L.-C.I.O., and his onetime protégé, Andrew L. Stern, the president of the Service Employees International Union, until now the largest union in the labor federation.
The split was sealed on Monday when Mr. Stern and James P. Hoffa, president of the Teamsters, announced that they were pulling their two unions out of the A.F.L.-C.I.O., just as the federation was beginning its 50th anniversary convention here.
Mr. Stern, 54, who is known for his eloquence, drive and impatience, had for months been pushing his membership, and the leaders and members of other unions, to break away, in a move he insists is needed to reinvigorate labor.
Deepening the rift, two other major unions, the United Food and Commercial Workers and Unite Here, which represents apparel, hotel and restaurant employees, are boycotting the convention and have indicated that they would also leave.
"We are in the midst of the most significant and profound transformative moment in economic history, and workers are suffering," Mr. Stern said at a news conference. "Our goal is not to divide the labor movement, but to rebuild it so working people can once again achieve the American dream."
Mr. Sweeney and Mr. Stern both say their overarching goal is to lift American workers, but they have different visions on how to get there. Mr. Sweeney, 71, has led the federation for a decade and prefers to work by consensus, nudging the federation's unions to do more organizing. But many have dragged their feet, and Mr. Sweeney says federation rules bar him from punishing them. For him, cooperation and solidarity are paramount.
Mr. Stern, on the other hand, wants far more aggressive recruitment efforts and the ability to crack down on labor leaders who fall short of organizing goals. Mr. Stern and his allies have called for rebating half the federation's budget to individual unions to spur organizing, but Mr. Sweeney protests that such a move would cripple the federation's efforts in political campaigns, job safety and other areas.
While Mr. Stern and his allies say their walkout is based on fundamental principles about what is the best course to help American workers and unions, their move has generated huge resentment and anger among other labor leaders. While Mr. Stern says he is charting a much-needed, more aggressive course for labor, other union leaders accuse him of a power grab and fault him for repeatedly rejecting Mr. Sweeney's offers of compromise.
"It is a grievous insult to all the unions that helped us," Mr. Sweeney said in his keynote speech to the convention. "But most of all, it is a tragedy for working people. Because at a time when our corporate and conservative adversaries have created the most powerful antiworker political machine in the history of our country, a divided movement hurts the hopes of working families for a better life."
Then, in a statement that won rousing applause and that many union leaders said was directed at Mr. Stern in particular, Mr. Sweeney said: "And that makes me very angry. The labor movement belongs to all of us, every worker, and our future should not be dictated by the demands of any groups or the ambitions of any individual."
The pullout by the two giant unions is a major blow to the federation, which until Monday had 56 unions and 13 million members. The departure of the Service Employees International Union, with 1.8 million members, and the Teamsters, with 1.4 million, takes away about one-fourth of the A.F.L.-C.I.O. membership. Those members paid about $20 million a year in dues, representing one-sixth of the federation's budget.
Standing alongside Mr. Stern at a news conference, Mr. Hoffa seemed to share his impatience. "What was done at the A.F.L.-C.I.O. was not working," he said. "We're going to do something new. That is our message."
The service employees' departure is a particular slap at Mr. Sweeney because it is a union that he headed before becoming the A.F.L.-C.I.O.'s president.
In recent months, Mr. Stern has voiced impatience that the labor federation and other unions have had so little success in recruiting members, while his union has jumped to 1.1 million members, from 900,000 a decade ago. That reflects the rapid growth in the service sector, for instance among janitors and nursing home aides, and also reflects the successful unionization tactics of his union.
Many union leaders agree that Mr. Stern has been emboldened to go his own way because of the service employees' singular success in organizing and because of the explosion in the service sector.
At the news conference, Mr. Stern said, "Today, S.E.I.U. is respectfully making its own choice to go in a different direction that we believe will work for working people."
Many labor leaders have openly said that they attribute Mr. Stern's departure to arrogance, to a "my way or the highway" approach and to a desire to head a new power bloc.
"This is not about change," said Leo Gerard, president of the United Steelworkers of America. "This is not about creating better lives for our children or grandchildren. This is nothing but a disguised power grab. They should be ashamed of it."
Officials involved in the negotiations that sought to prevent a schism said some union presidents so disliked Mr. Stern that they had pressured Mr. Sweeney not to grant meaningful compromises to him.
At the same time, Mr. Hoffa and Joe Hansen, the president of the food and commercial workers' union, said Mr. Sweeney had shown far too little willingness to make compromises to prevent unions from quitting the federation.
One issue that separates the sides is how much of the federation's money is spent on recruiting workers. Mr. Hoffa often asserted that the A.F.L.-C.I.O.'s leaders were spending too much on politics and not enough on organizing.
"They dramatically increased the amount of money to throw at politicians," Mr. Hoffa said on Monday.
But Mr. Sweeney and his allies argued that it was important for unions to spend generously to elect politicians who might help create a climate favorable to unions and union organizing.
Even as Mr. Stern and Mr. Hoffa seceded, they adopted some conciliatory language, saying their unions would not raid other unions to try to recruit workers. And with many Democrats and union officials worrying that the schism in labor would weaken labor's effectiveness politically, Mr. Stern said he hoped to continue cooperating with the A.F.L.-C.I.O. on politics. Among Democrats, there is considerable fear that the labor split will undercut the A.F.L.-C.I.O.'s role as a highly effective coordinator for the nation's unions in lobbying and political campaigns.
"There's a lot of anxiety any time one of your principal allies is split, especially given the amount of resources that the other side has amassed against us," said David Axelrod, a Democratic consultant. "The White House, the Republican Party, would like nothing better than to put labor out of business as a political force."