Farm Unrest in Mexico Challenges New President
Mexico's small farmers are being battered by explosion of free trade under Nafta, plummeting market prices and cuts in government support; they complain that free trade accord has not given them access to American markets they were promised, and has forced hundreds of them out of business; tens of thousands of farmers hold protests around country, including 5,000 sugar cane farmers who converge on capital and block access to government offices; for Mexico's new president, Vicente Fox, reforming agricultural industry and finding alternative employment for millions of subsistence farmers at time of widespread resentment may prove his most important domestic challenge; photos; map (L)