WASHINGTON -- AFL-CIO President John Sweeney said yesterday that if the labor federation splinters on the 50th anniversary of the merger of the American Federation of Labor and the Congress of Industrial Organizations, it "would be devastating" but not the death knell of the labor movement.

The 71-year-old Sweeney, who won the presidency of the federation in 1995 by challenging the so-called old guard of Lane Kirkland and Tom Donahue, is seeking re-election at the AFL-CIO's annual convention that starts July 25 in Chicago. He expects to win but acknowledged a far bigger fight looms if five or more of the federation's most active unions pull out as they have been threatening to do.

The dissidents are being led by Andrew Stern, who succeeded Sweeney as president of the Service Employees International Union (SEIU). The United Food and Commercial Workers International Union and the International Brotherhood of Teamsters also are considering leaving.

The showdown comes as the clout of unions continues to dwindle. Unionized workers represented 30 percent of the work force 50 years ago; today, they account for about 12 percent, or 13 million, as lower-skilled industrial jobs have gone overseas and large retail companies such as Wal-Mart have gone unorganized.

"I've done my damndest to do what I can to keep unity," Sweeney said at the breakfast meeting, adding that he hopes the federation will be preserved but can't guarantee it. He said "conservatives are just gloating over" the possibility of a split in big labor and that many employers "can't wait for that to happen."

Stern and other union insurgents argue that the AFL-CIO has become stodgy and isn't doing enough to organize new members. They want more resources spent on organizing -- the 900,000 member SEIU boasts that it spends half its total resources on organizing and says that should be a model for the federation's 57 affiliated unions.

Sweeney argues that 30 percent is a more realistic figure and says that unions must not divert their attention from the political arena even though they have lost battle after battle in Congress on their issues and were unable to get Massachusetts Sen. John Kerry elected president last year. If each union put up 30 percent of its resources, he said, there would be $500 million for a new organizing campaign.

Stern has set up a Web site, www.unitetowin.org, to push his agenda. It argues that the fight is over whether the labor movement continues to get "smaller and weaker while global corporations get larger and stronger" and vows to build a new alliance to "win good jobs, affordable, quality health care, opportunity for all and retirement with dignity.

Sweeney contends he is fighting for the same things and, taking a page from Stern's Web site, agrees that the Bush administration is the "most anti-union" administration in U.S. history. But he claims the AFL-CIO must stay active politically, which to him means supporting Democratic candidates even though at least a fourth of his union's members are Republicans.

Sweeney concedes the irony of having led an insurgency 10 years ago and now being the target of one himself. "What I said 10 years ago wasn't about who headed the federation but ... that it was time for a healthy change."

This time, he insists, the changes being contemplated by his opposition would not be healthy. "To pick up your marbles and leave the game is not productive," he said.

"I'm still hopeful because the stronger and more united the labor movement is, the more effective we can be. The differences between us are not that great."