In Moscow this past week both Ronald Reagan and Mikhail Gorbachev said that we are living in a ``new era'' - and both of them are correct. The summit in Moscow did not in itself bring a ``new era'' into existence, but it did identify the fact that one has arrived.
It has come about for many reasons, of which the most influential is probably that the United States is less afraid of the Soviet Union in 1988 than it was in 1980, when Mr. Reagan won the presidency.
A second reason is that the leaders of the Soviet Union have come to realize that living in a state of hostile isolation from the outside world has cut them off from the technologies of that world. They were running the risk of becoming a technologically obsolete county. In the long run, that would undermine their military position.
Mr. Gorbachev has recognized both factors. Since coming to power in Moscow three years ago, he has worked steadily to undo or temper those features of Soviet policy and behavior which have caused the outside world to fear, distrust, and arm against the Soviet Union.
The presence of Mr. Reagan inside the Kremlin itself, on the stage at Moscow University, strolling around Red Square exchanging friendly chatter with Mr. Gorbachev - all testify to the fact that the President's countrymen have come to view the Soviet Union through a different lens.
In 1980 they saw an expansionist military power still pushing its ideologies on every continent and even into Central America. By 1988 they were seeing a country in economic difficulty, withdrawing its troops from Afghanistan and Mongolia, and talking about pulling some of them back from Central Europe.
And by 1988 Mr. Reagan's countrymen had learned that the leader in Moscow has political problems. His tenure in power is uncertain. His policies are being resisted. He too is of human scale, with the same kind of political problems which beset modern political leaders in Western countries.
Mr. Gorbachev has demystified and de-ogreized the Soviet Union. In Moscow this week Mr. Reagan agreed that it is no longer an ``evil empire.''
So the world is in a ``new era'' in which the US and the Soviet Union can do routine business with each other and solve such mutual problems as are soluble by reasonably common action.
But how far will this go and how long will it last?
There was anxiety in other places. Arabs were worried that Mr. Gorbachev would be less interested in protecting them against Israel. NATO's secretary general, Lord Carrington, was anxious lest this new reconciliation between Moscow and Washington might lead to lagging support for NATO.
Everyone is careful to avoid using the world ``d'etente'' even though this is the second time since World War II when that word of specific diplomatic meaning could accurately be applied to US-Soviet relations. This is, beyond serious doubt, the beginning of a second ``d'etente,'' which has been made possible by the Soviet withdrawal from Afghanistan and the change in the American view of the Soviet Union.
It is reasonable to think that it will last as long as Mikhail Gorbachev remains in control in Moscow. It could be passed along to his successor. It could also be upset tomorrow if the political opposition to him should win out in the next round of confrontation inside the Central Committee of the Soviet Communist Party.
The odds probably favor a continuation. Mr. Reagan is nearing the end of his presidency, but his new opening to Moscow, his presence there this past week and exchange of the documents there with Mr. Gorbachev are all approved by George Bush and Michael Dukakis, one of whom is virtually certain to be the next president of the United States.
One can hardly conceive of either a Bush or Dukakis administration rejecting the ``new era,'' unless there is drastic reversion in Moscow to confrontation and hostility.
If the ``new era'' is spoiled, the spoiling will probably come from events in Moscow.
Unless or until that happens, the chances are that there will be an opening up of traffic between East and West in ideas, technology, and goods.
There is also likely to be a decline in the number and intensity of the ``proxy wars'' which have been characteristics of periods of tension in East-West relations. The temporary truce between the ruling Sandinistas and contras in Nicaragua was extended this week, largely because neither Moscow nor the US is giving its clients the weapons needed to keep fighting. There are new negotiations under way pointing toward a possible settlement for both Angola and Mozambique. Vietnam says it is going to withdraw its troops from Cambodia.
There is a ``new era.'' It can last for a good while. It will make the world a little safer. The first ``d'etente'' lasted for seven years (1972 to 1979). This one, being more soundly founded and with fewer illusions, should last at least as long. It could last longer.