Boycott Gallo Wines: Cesar Chavez, leader of the United Farm Workers, is coming to Cambridge to help put a full-scale Boston-area boycott of Gallo products into high gear. The UFW leader, who has guided a long battle to win the rights of California farm workers, will take part in a demonstration Saturday at 1:30 p.m. by the Fresh Pond Shopping Center. Last year Gallo signed a sweetheart contract with the Teamsters in an effort to escape facing a struggle with the UFW over workers' rights, but the tactic hasn't been very successful. The Gallo boycott has had its initial effects, but Ernie and Julio need a little more friendly persuasion. Chavez will try to raise some money for his union Saturday night at a $5-a-plate dinner being held at Boston College's Roberts Center. Arnold Miller, president of the UMW, and folksinger Phil Ochs will also attend the fundraiser, scheduled for 8 p.m.