THE results of last week's mid-term elections in Mexico indicate a vote of confidence for the free-market economic reforms of President Carlos Salinas de Gortari.These results, like past ones, are marred by widespread claims of electoral fraud. Thus Mexico's political dilemma goes on: a reformist, forward-looking president at the helm of a party, the Institutional Revolutionary Party (PRI), which has a long record of unchallenged rule and ballot-box manipulation. The country's economic opening is real; its political opening, to genuine multi-party competition, should be just as real. Although some observers feel the recent elections were in fact cleaner than most, the charges of fraud should be thoroughly probed. In any case, there are clear reasons why most Mexicans may have chosen to back PRI candidates who will support Salinas's program. Since his narrow, highly controversial election in 1988, the president has loosened the statist, bureaucratic hammerlock on the Mexican economy. He brought inflation down from more than 150 percent a year to around 16 percent. He has increased trade, forcing Mexico out of the economic nationalism that hampered its commerce with the rest of the world. A central theme of Salinas's has been a closer relationship with the United States. The free-trade agreement being hotly debated in Washington is his keynote, and Mexicans have generally bought into the idea that their economic future hinges on partnership with the US. This after generations of suspicion about Washington's motives, fed by long historical experience. Those suspicions could revive; the politics of free trade could be stormy. But for now Salinas seems to have a mandate to pursue the agreement with the US, as well as such internal goals as privatization, through the remainder of his six-year term. His opponents on the left are in disarray, while Mexico's right is hard put to say how its policies would differ from those of the president. Does this mean Mexico's political opening is indeed threatened by renewed PRI preeminence? The forces of economic and political diversity, now set loose, should prevent that.