THE world may still be a dangerous place, but the most urgent threats to American democracy and national strength are now at home. So runs an argument emerging in recent weeks from some prominent foreign affairs thinkers.The cold war and the Gulf war have established the supremacy of American military power. Now - according to these theorists, some of them former high officials - the United States needs to turn inward to shore up its strength. This recent spate of look-homeward views was started by William G. Hyland, editor of Foreign Affairs magazine, who wrote a little over a month ago that "the United States has never been less threatened by foreign forces than it is today,... but never since the Great Depression has the threat to domestic well-being been greater." Mr. Hyland figures that winning the cold war has earned the US about a decade to shift attitudes, attention, and money from foreign concerns to domestic. Peter G. Peterson, chairman of the Council on Foreign Relations, has written a paper that puts the domestic agenda first. Mr. Peterson is a former US secretary of commerce and senior adviser to President Nixon on international economic affairs. The thrust of his paper was endorsed last month by the American Assembly, a bipartisan conference of foreign affairs and national security officials and experts. American weakness in investing in productivity, educating the young, and absorbing a growing underclas s, he wrote, "may have a greater direct impact" on the integrity of American institutions and values "than the threats from abroad." Similar views have been propounded in the weeks since by Leslie Gelb, a foreign affairs columnist for the New York Times and former State Department official, as well as David Gergen, a U.S. News & World Report commentator and former communications director in the Reagan White House. Many Americans have long argued for spending more money and attention on solving domestic problems and less on defense and foreign aid. The new twist is that it comes from people whose main concern is foreign affairs and nat ional security. Frank Fukuyama, a Rand Corporation consultant who recently left the State Department, has argued that most American foreign policy problems can be traced ultimately to the American education system and the lack of economic competitiveness of the work force. Other national security experts are skeptical of this domestic thrust. Some believe traditional military threats remain the most dangerous. Fred Ikle, a senior national security official in the Reagan administration and now an analyst at the Center for Strategic and International Studies, argues for caution. "Many people get it the wrong way around," he says. "We've been able to start reducing the defense budget because we've paid a great deal of attention to national defense." Cutting too much too soon could draw military competitors, such as the Soviets, back into the field, he adds. Some believe that America's global role presents opportunities too great to withdraw from. "We've helped to create a better neighborhood out there. If after all that effort we turn our backs because we still have serious problems at home, that would be a great tragedy," says Henry Nau, a George Washington University political scientist and author of "The Myth of America's Decline." Professor Nau sees global opportunities and domestic problems as inseparable. To fail to invest in Eastern Europe because of urgent concerns at home, for example, is to accept a "false division" between foreign and domestic affairs, as well as to miss an opportunity to achieve in the East "what we've achieved in the West." Francis Bator, a longtime leading scholar on these issues now a professor at Harvard's Kennedy School of Government, deems the new national security argument for the domestic agenda about two-thirds right. "The president of the United States had better start paying serious attention, not just rhetorical attention and fluff, to some domestic concerns," he says, especially education and investments in future productivity. "Our quality of life at home, I think, is in serious trouble." Professor Bator does not accept, however, that this requires diverting resources from concerns abroad or that the domestic economy will present a threat to national security in the foreseeable future. The United States remains the wealthiest country per capita in the world and one of the least taxed, he notes, so it has no need to choose between a world role and domestic concerns. "We ought to do both," he says.