In the early years after the Sandinistas came to power in 1979, Nicaraguan President Daniel Ortega would come to the United Nations in full military uniform, with slicked-down hair, steel-rimmed glasses and harsh language punctuated by karate chops. Now Ortega sports the blow-dried look, fashion glasses, a cashmere sweater and a well-cut civilian suit. His rhetoric has changed as much as his appearance. Today he speaks softly and sometimes attempts wry jokes.

Ortega has learned to look and sound like the new style of Communist ruler, like a Gorbachev or a Zhao Ziyang. These well-tailored new Bolsheviks look like modern men and often sound like them as well. When they speak to the outside world, they avoid the Marxist jargon and polemics that once marked the Leninist style of politics. They no longer speak -- to us, at least -- of ''burying us.'' Nor do they publicly counsel others to ''cast off the shackles of imperialism.''

More and more often, as they discuss arms reductions or the Central American peace plan, they sound like reasonable men committed to building a safer world. They have become expert practitioners of image politics. And more and more it seems downright churlish to doubt the good will of these manifestly reasonable men -- especially since we Americans want so badly to believe them.

Almost every American longs to end the state of mutual distrust and disrespect that has characterized U.S.-Soviet relations since World War II. Americans hate spending large amounts of money on armaments. We dislike permanent alliances and are dismayed at the thought that we have real enemies. And so we welcome with enthusiasm every evidence that Soviet or Nicaraguan leaders are ''mellowing'' with time. The smallest move to free-market strategies in economics, to liberalization in domestic affairs, to a less expansionist foreign policy is greeted with relief and optimism.

The fact that we believe in change and embrace it makes it much easier to believe that other countries will change as well. While Marxists think history is governed by inexorable laws, we believe men (and sometimes women) make history and can change it. So we take every change in leadership seriously, especially when generational change also is involved and is accompanied by a change in style.

Whether a new generation has come to power, as in China or the Soviet Union, or the same leaders speak in new tongues, as in Nicaragua, we explain to each other that ''the pressures of reality have had their impact''; that the responsibilities of power have ''mellowed'' the leadership; that revolutions and revolutionaries ''always moderate'' given time and experience. We applaud and magnify the evidences of change and we wonder aloud and obsessively how we can help.

We try not to notice when such events as the demotions of reformers Hu Yaobang or Boris Yeltsin suddenly call into question our hopes for imminent democratic transformation, and for greater openness and tolerance.

Our optimistic reactions to welcome trends are manifestations of the American national character. They are shared by both parties, by Ronald Reagan as well as Jim Wright. And the danger that imprudent decisions will be based on our hopes is also bipartisan.

In thinking about arms agreements and Central American peace plans -- as policy-makers are these days -- responsible people in both parties urgently need to face the harsh facts that we do not really know Mikhail Gorbachev's intentions vis-a-vis his country or our own, that we do not really know how great his power is within his government, how long he can maintain it, or by whom he might be followed. We do not know why there were sudden shifts in his decisions on a summit meeting in Washington or why he so harshly attacked his close associate Yeltsin. We do not know if his new line on war, peace, capitalist evolution and on the relations of the Soviet Union with Eastern Europe presage permanent changes in policy or are only shifts in verbal tactics.

With regard to Central America, we do not know if the Ortegas and the FSLN have any serious intention of providing to their people the freedoms they have promised, or if they are merely maintaining a facade of liberalization until the U.S. Congress has forced the dismantling of the contras.

These are extremely important questions. Americans should not permit themselves to make substantive decisions on the basis of style.

There is finally only one way to judge the promises of the new Bolsheviks. It is how they use force against those weaker than themselves. Rulers who use force to subdue opponents, conquer neighbors and intimidate allies can hardly be expected to treat the rest of us differently.