Andy Stern and John Sweeney offer clashing tones on the Democrats, their convention, and their candidate: "It is a hollow party," Stern said, adding that "if John Kerry becomes president, it hurts" chances of reforming the Democrats and organized labor...Later in the day, AFL-CIO president John J. Sweeney told The Post that Stern's attitude "is not justified." Sweeney, also a product of the SEIU, the largest and fastest growing union within the AFL-CIO, said the process of change is already under way within labor, adding that he is impressed with "the unity and solidarity" of Democratic support for Kerry. "I'm optimistic about the future of the Democratic Party," he said. ...Stern complained that motivating blue-collar families who have not voted in the past is being impeded because Kerry and the Democrats have declined to address what he calls "the Wal-Mart economy," a system in which he says employers deliberately keep wages so low and hours so short that workers are forced to turn to state Medicaid programs for their families' health care. He also criticized what he called the vagueness of the Democratic platform on trade issues. Sweeney said he thought both complaints were off-base. He said Kerry had offered a very specific health plan with real benefits for working families. And he said he was confident that, despite his history as a supporter of liberal trade agreements, Kerry was sincere in promising to include "core labor standards" in future negotiations.