The other day, with a heroic portrait of irascible old Andrew Jackson gazing down on him in the Oval Office, a benevolent president, mellowing through the last months of the longest presidency since Ike's, expounded to four journalists on his benign view of the world. I have heard him purr like this before. Then as now his subject was world peace.

Back in 1984 Ronald Reagan met with several of us in the White House library. He was tired from the campaign trail, and he stumbled ineloquently over several burning issues of the hour. But on one issue his utterances were explicit and even vivid: his hope for an arms control agreement with the Soviet Union. His interest in this sort of thing is not sudden.

Now he has his agreement. Twenty-four hours before our latest interview, he signed a pact with Mikhail Gorbachev to eliminate all intermediate-range missiles from Europe. Seated in the Oval Office, he looks the part of a leading man. His 76 years are not evident. He is fit and alert. His eyes, though red-rimmed, twinkle as he goes through a range of emotions: joviality, confusion over his critics, pique over right-wing impudence, magnanimity -- but, trust me, none of that adolescent euphoria that the Washington press corps keeps looking for. Rather his mood is benign.

What brought this renowned hawk to negotiations with Gorbachev were three perceptions. Reagan has long perceived Mutual Assured Destruction in response to Soviet aggression as an immensely dangerous strategy. He perceives Gorbachev as a unique Soviet leader. And some time ago he perceived that his policy of military buildup and tenacity at the bargaining table had brought the hour for an agreement at hand. In 1983, over the opposition of various species of anti-nuclear activists, the United States brought intermediate-range missiles to Europe, responding to the Soviets' unprovoked deployment of their SS-20s. Then, by 1987, Reagan saw that it was possible to return Europe to the status quo before deployment.

The president's alarm over MAD, of course, was what initially inspired him to pursue a space-based defense -- "Star Wars." He has been reiterating his alarm for years, and the other day he termed the MAD strategy "uncivilized." He hopes the present INF treaty will be instrumental in moving the United States away from MAD, though he recognizes that the present imbalance in conventional force in Europe must be eliminated, and he still is avid for Star Wars.

Equally important in the president's decision to meet and conclude this agreement with the Soviets is his sense that Gorbachev is different from past Soviet leaders. Of the four who have ruled in Moscow during the Reagan presidency, "this is the first Soviet leader that has openly discussed . . . that there are flaws in their economic system" -- and with ill-concealed pride, Reagan mused that glasnost might "partially confirm some of the things that I said before about their system."

Moreover, Reagan thinks it significant that "in the past, Soviet leaders have openly expressed their acceptance of the Marxian theory of the one world communist state." Gorbachev, the president went on to say, "has never said that." And next year Gorbachev will allow Russians "to observe the millennium -- the thousandth anniversary of the baptizing of a Christian in . . . Russia."

Finally, he feels that his policy of "strength and realism" has been vindicated. So maybe it is appropriate that Old Hickory gazes down on him in the Oval Office. President Reagan believes that he has been tough and that he has prevailed. But as our interview trailed off into suspicions uttered about his motivations he worried aloud that the record of his foreign policy as well as his domestic achievements would be lost to history owing to an "inaccurate" press. His apprehension is legitimate.