Presidents of unions representing more than 60 percent of the AFL-CIO's members stood up for John Sweeney Monday, backing his candidacy for another term as AFL-CIO president. Sweeney called for solidarity in a labor movement torn by threats of several unions , including the two largest, to leave the federation if reforms they support aren't adopted. Sweeney said only labor' enemies are cheering over the prospect of a split and the millions of workers who depend on unions need a united labor movement.