Guess Inc., the biggest clothing maker based in Los Angeles, warned investors that it will only break even or perhaps post a modest loss for the fourth quarter. That would be down from analysts' profit projections of nearly $7 million, or 16 cents a share. Guess blamed its disappointing results on sluggish wholesale sales, weak retail sales stemming from a labor union publicity campaign against the company and lower-than-expected licensing revenue, especially in Asian markets. Guess also said that Ken Duane, president of worldwide sales, is leaving the company by mutual agreement with management. His duties will be assumed by the company's new vice president of sales, Nancy Shachtman, who previously was merchandising vice president. Guess' announcement came after the close of trading on the New York Stock Exchange. Shares closed unchanged at $6.13.