President Reagan, in publicly opening the door to a summit meeting with Soviet President Chernenko, has taken a significant step toward easing East-West tensions.
Whether the two leaders will readily proceed through that door remains to be seen. But the American public, the Western allies, the leaders of the President's party, and many of his advisers think Reagan and Chernenko should move toward a meeting. And so do we.
Mr. Reagan has eased his requirements for a summit. He now says a meeting need not be conditioned on arms talks progress. There need be no guarantee that a specific agreement or set of agreements would emerge; a ''general agenda'' would now suffice. He suggested, at his press conference last Thursday, a more casual approach might do: ''If (the Soviets) agree with me that there are things we can talk about that might clear the air and create a better understanding between us, that's fine.''
These changes in his public position are to be welcomed. They follow a shift earlier this year toward a more forthcoming US posture on the adjourned intermediate and long-range arms talks at Geneva. It could well be that a summit could offer the Soviets a way out of the arms-talks box they have put themselves into: They have demanded that the new NATO Pershing II missiles be withdrawn from Western Europe before talks can be resumed, a demand the US President cannot accept.
There is plenty to talk about at a summit besides arms. The Soviets purportedly want a specific agenda, with items of agreement set in advance. Such items should not be hard to find. Trade, cultural exchanges, sea treaties - even an agreement to protect the Olympics and other athletic competitions from future political boycotts - offer enough grist for communique-initialing to satisfy any ceremonial appetite on either side.
However, the need of the moment is not to sign new international pacts. It is to reassure the East and West halves of the world that civil communication can be restored between the dominant powers. No more disparaging the Soviet system as ''Mickey Mouse,'' or the American observance of Memorial Day as a ''militaristic orgy.''
At the same time, the West should not be naive about what a summit would achieve or how the Soviets might attempt to manipulate it. The Soviet Union does routinely interpret bilateral agreements to its advantage, while claiming it is the US that reneges. Time, too, is an element. The White House has maintained that four to six months are needed to prepare for a summit - this would take it right up to election time and beyond, depending on how far along negotiation with the Soviets has already proceeded.
A ''get together'' summit might be the easier and safer to arrange. The Western economic powers learned a lesson at their Versailles meeting two summers ago when the Reagan administration was rebuffed in trying to exact agreements from its allies. It could prove wiser to resume face-to-face talks between the East's and West's leaders after a five-year lapse without the burden of too precise expectations.
Will the Soviets want to meet? The Soviets will have to calculate for themselves how movement toward a summit would affect their future negotiations with Mr. Reagan or his successor after the US election. Reports of a crisis of confidence in the Kremlin leadership might be exaggerated; either way, a summit with the American President, or his successor, could help reinforce the Kremlin's claim that it preeminently seeks peace in the world. Dragging its feet would undercut that claim.
President Reagan, in saying the door is open to a summit, was not exactly standing in the doorway and beckoning energetically for the Soviets to come on in. He did not go as far as his Democratic opponents, who have called for regularly scheduled, yearly summits.
But if he is judged by his words, he now is willing to risk being spurned on a summit and to engage the Soviet President in direct talks about world affairs. This is progress on one side of the world divide.