THE flight across the Baltic Sea from Helsinki, Finland, to Tallinn, Estonia, takes only a few minutes. In the past, this route crossed the Iron Curtain, but now runs from one free nation to another. As the first senator to visit the Baltic states since the failure of the Moscow hard-liners' revolt, I looked forward to seeing the people and conditions there.Fifty-one years under the Soviet boot have left ugly stains on Estonia, Latvia, and Lithuania. Socialist enterprises and central planning have raped the environment. Forests were slashed and burned, marshlands are poisoned by toxic wastes, the air is filthy from factory smokestacks, and fresh water supplies are threatened. It will take decades to clean up. Economically, the Baltic states were the strongest of any Soviet-controlled areas. Yet they are suffering from decades of state-run industries and centrally controlled efforts to prop up the Soviet economy and military machine. Few of these plants can be made profitable, so few investors will be prepared to buy them from the government. The Baltic states were dependent on Soviet resources, markets, and what passes for Soviet technology. This cycle must be broken. Everywhere I visited, average citizens and leaders approached me about their need for United States assistance - the requests were in the billions for the Baltic states alone. I had to tell these people that I do not believe the United States can or should pump billions of taxpayer dollars into Latvia, Lithuania, and Estonia. Instead, with Western encouragement and realistic help and advice these jubilant new states must promote their own prosperity. And if this is true in the Baltics, it is much more th e case in other republics that have recently declared independence from the Soviet Union. It hurt me to see looks of disillusionment as I described these realities. But the US cannot afford a massive "Marshall Plan" for the Baltic states or other former Soviet republics, given our own deficit and debt. US public spending habits now may be a greater threat to our country than Soviet military might. Americans will, as we always do, respond generously to humanitarian needs created by the lack of private property rights and the existence of collective farming. Food and medicine will be needed as another brutal winter approaches. But Americans cannot transform the Soviet economy. Our know-how and technical assistance will help, but the principal burden will fall upon the new nations themselves and the other republics that maintain some kind of loose union. It is wrong for the US to give government-to-government cash, either on our own or through multilateral institutions. Plowing money into a failed socialist economic system is a recipe for disaster. The whole system must be scrapped. The harsh reality is that foreign aid has not produced prosperity anywhere. A better investment would be to provide management skills and entrepreneurial training to the Baltics and to others. As Congress considers ways to encourage and help the liberated areas of the Soviet Union, our first responsibility is to the American taxpayer. Free trade, technical assistance, aggressive promotion of American investment in the Baltic states, US Information Centers, food, and humanitarian aid should be the cornerstones of our policy.