Autumn being the season of mists and mellow fruitfulness, as Keats would have it, it is only fitting that there be increasing talk about fruitful bipartisanship in our foreign policy.

A misty softening in the administration's ''verification'' terms for an intermediate-range nuclear weapons agreement with the Soviets is one example. Another is said to be reflected in Congress' mellowed reluctance to challenge forcefully the administration's naval intervention in the Persian Gulf.

But the evidence of ripening bipartisanship most often cited is the seeming collaboration between President Reagan and House Speaker Jim Wright on a plan for peace in Central America. In a recent column, Henry Kissinger blows this illusion away. The Reagan-Wright compromise, he rightly argues, in no way corresponds to the ''true bipartisanship'' at work from ''the Truman Doctrine in 1947 till roughly the Vietnam War when there was substantial agreement on foreign policy objectives. Disagreement concerned means.''

Today ''exactly the opposite is the case. . . . Bitter antagonism over objectives remains.'' His evidence is irrefutable.

Few would deny that Ronald Reagan is hell-bent on somehow transforming the Sandinista government into a pluralistic democracy. Even fewer would quarrel with Kissinger's point that ''the contra aid so far requested could not achieve the administration's stated objectives by military means; it would be at best enough for a prolonged stalemate.'' Similarly, few would challenge Kissinger's claim that most opponents of contra aid are unprepared ''to take the responsibility for perpetuating a Marxist-Leninist regime in Managua unconstrained by either security restrictions or human rights provisions.''

It is hard, then, to escape Kissinger's conclusion that unless this conflict over ends as well as means is resolved, ''we will slide into a situation where policy is suspended between a search for victory with insufficient resources and a call for diplomacy drained of incentives.''

To confuse this with ''true bipartisanship'' is to misremember what ''true bipartisanship'' was all about. It was nothing so puerile as the notion that ''politics stops at the water's edge.'' If it did, we would not have presidential candidates airing their own foreign policy approaches on world tours, summit meetings and state visits tied to electoral timetables and congressional junketeering.

The truth is that when presidents promise or plead for ''bipartisanship'' (as Reagan now does), what they mean more often than not is: do it my way. A better word might be nonpartisanship. But this can only begin with a shared sense of the nature and the gravity of a threat. It requires a willingness to accommodate partisan and ideological differences, not only between political parties but within them and not only within Congress but within the executive.

Nothing better illustrates the rarity of this state of grace, or the limits on what it can achieve, than Kissinger's definition of what would be ''true bipartisanship'' in Central America. Given the time remaining to the Reagan administration, Kissinger would ask very little of ''true bipartisanship'' in Central America. He proposes an agreement to extend contra aid at present levels for another 18 months so that a new administration can ''set its own policies.''

He would have both sides agree, as well, that the U.S. peace plan should put more emphasis on the removal of the Soviet presence in Nicaragua and that the Guatemala City plan should be more precise in its insistence on ''democratic institutions.''

That should be enough, he seems to believe, to ensure that ''an issue of fundamental national consequence'' will not be ''overwhelmed by the politics of an election year.''

On the contrary: having resolved none of the gut issues that Kissinger himself so ably analyzes, Kissinger's plan would be an invitation to the full flowering of partisanship, in its true sense. Surely somebody, in the course of the presidential campaign, is going to ask the candidates about the means as well as the ends of the Central American policies they would practice as president