The Service Employees International Union yesterday took the first concrete step toward breaking up the AFL-CIO, the nation's central labor federation.

The SEIU executive board, at a meeting in San Francisco, authorized union leaders to quit the federation. As many as four other unions -- the Teamsters, the United Food and Commercial Workers, Unite Here and the Laborers -- could follow suit, pulling out 5 million of the AFL-CIO's 13 million members.

The conflict could become a major battle at the AFL-CIO convention at the end of July in Chicago, with both camps so angry that prospects for a peaceful resolution appear unlikely.

Democratic Party officials have privately voiced deep concern over the struggles within the AFL-CIO, which has become a mainstay of the party both financially and in voter-turnout drives.

The five dissident unions, which together represent about 40 percent of the AFL-CIO's membership, have been calling both for the replacement of President John J. Sweeney and for changes in the structure and powers of the 58-union federation.

The major complaint against Sweeney is that he has not stemmed the loss of union members. He has overseen a politically stronger labor movement, but the unionized share of the workforce has continued to decline, falling to 12.5 percent overall last year, and 7.9 percent in the private sector.

The SEIU executive board yesterday approved a resolution declaring: "There comes a point where if we can't reach agreement on basic principles, we should each move on and devote our time and resources to a strategy we believe will help working people win -- while still working together on political and community issues we share."

The executive board of the United Food and Commercial Workers International Union plans to discuss the possibility of disaffiliation with the AFL-CIO on Tuesday.

The dissident unions had been exploring the possibility of having John W. Wilhelm, president of Unite Here, challenge Sweeney for the AFL-CIO presidency, but they have been unable to win majority backing.