SENDING United States Marines to restore the Rev. Jean-Bertrand Aristide to Haiti's presidency is a final option. For now, tightening the noose of economic sanctions as mandated by the Organization of American States, the United Nations General Assembly, and President Bush is the most appropriate approach.The Western Hemisphere's overriding concern must continue to be the nurturing of democracy in Haiti. Late last year, in Haiti's first-ever fully free and popular election, Rev. Aristide won an overwhelming mandate, receiving 67 percent of the votes cast. After nearly three decades of dictatorial rule by Francois (Papa Doc) and Jean-Claude (Baby Doc) Duvalier, and nearly five years of corrupt and stuttering military rule, the wildly acclaimed victory by Aristide's radical forces signaled the beginning of Haiti's modern renaissance. With solid Western backing, particularly from the US and France, Haiti had its best chance in modern times to begin developing itself economically and politically. Haiti is the poorest and, by most indicators, the most backward country in the Americas. Its 6 million inhabitants have rarely known prosperity, good education, suitable health care, or freedom from political extortion. Aristide's accession to power early this year brought new hope and, among the underprivileged in the slums of Port-Au-Prince or in the countryside, a sense of exhilaration. But, as far as the Army and the wealthier classes in Haiti were concerned, Aristide overreached himself. He exerted a measure of new control over the Army and curtailed many of its perquisites. He made commercial life more uncertain for businessmen. Unfortunately, too, in speeches he enjoyed rabble-rousing more than persuading, and even praised vigilante rule and some aspects of mob violence. He was less a voice of tolerance than a threatening voice of mass rule. Despite these seemingly anti-democratic tendencies, and some alleged attacks on ex-Duvalierists, Aristide did not openly abuse his high office. But merchants and the Army suspected dictatorial tendencies, particularly after he began recruiting and training his own special guard. Prompted by Aristide's supposedly inflammatory rhetoric, his continued antagonism to the old ruling groups, and the formation of the new guard, the Army ousted him in late September and sent him into exile. In the manner of pre-World War I Haiti, too, the Army physically held the country's new parliament hostage until its members voted to annul Aristide's election and install Chief Justice Joseph Nerette as acting president. BETWEEN 1908 and 1915, Haiti had seven presidents and about 20 uprisings and attempted insurrections. One president and about 300 members of his guard were blown up in the palace. Another was poisoned. A general formed an Army and marched on the capital from the north, precipitating an eight-month-long civil war. There were massacres and counter-massacres. The US marines intervened and ruled Haiti from 1915 to 1934. The current leaders of Haiti's Army claim that they are not really ruling, and want new elections. But Haiti's democratic experiment will surely die if Aristide, its rightful leader, is not restored. Given that democracy took so long to come to Haiti, and that its real seeds were planted so laboriously, the leaders of the Western Hemisphere must continue to back him and it, and to ensure that sanctions work. Intervention can only be a last resort. Given Haiti's dependence on the export of assembled piece goods, like baseballs and textiles, and imports of petroleum from some of its neighbors and the US, economic sanctions should soon bite. The military junta that may be ruling will not easily know how to circumvent those sanctions. But President Bush will want to make sure that none of Haiti's immediate neighbors continue to trade, and that France, Canada, and Venezuela do the same. Equally, when Aristide returns to power, those who assisted his return must find the means to influence and improve the worrying way in which he governs. Aristide's revolutionary zeal needs to be, and can be, channeled into effective national, rather than personal, forms of leadership. Then he can continue to preside over the flowering of Haiti's new participatory government and to use his enormous popularity to bring a measure of real prosperity to the country. This must be the goal of the United States.