THERE IS a tendency in assessing summits to tote up the items agreed on and the items not agreed on, and by this calculation the Bush-Gorbachev summit was only a modest success. With the exception of important new restrictions on chemical weapons, the subjects agreed on -- aviation and maritime matters, student exchanges and the like -- were in the category of useful but not central. On the large questions of Germany and NATO, Lithuania and the Baltics, strategic arms control and conventional force reductions in Europe, deep differences remain. The commercial pact the two leaders signed hinges on a tariff break for the Soviets that President Bush won't ask Congress to give until Moscow completes a new emigration law -- a matter itself clouded by Mideast developments -- and that is also tied politically to Lithuania. The atmospherics were, by the measure of some earlier summits, restrained.

Still, it would be an error to apply the old means of measurement as though nothing had changed. (Could anyone have imagined a year ago that this spring the summit issue for the United States would be whether a united, democratic Germany would be permitted to remain in NATO?) There is an identifiable new aspect to superpower relations in the Bush-Gorbachev period. Not so much the recorded achievement of the summit as its ambitious reach is a fairer measure of what went on in Washington. The diminution of the old sense of imminent danger and inevitable confrontation has released both sides to deal with a broader and deeper agenda. The leaders are tackling difficult and sensitive subjects touching the vital interests of their countries. Not that Mr. Bush is unmindful of political pressures at home, but the fact is, moreover, that the Soviet Union is in incredibly tumultuous internal transition -- so tumultuous as to have finally reduced Mr. Gorbachev, in American eyes, to the proportions of a mortal politician.

The two men are said to call each other ''President.'' The personal detachment seems to fit the evident mutual effort to, as Mr. Gorbachev put it, take into account each other's concerns even when the two disagree. In this spirit, for instance, Mr. Bush made specific proposals to meet some of the Soviet's objections to his insistence on keeping Germany in NATO; the matter will require much more discussion. Invited to locate superpower relations on an adversary-or-ally spectrum, Mr. Bush said he didn't know how to ''quantify'' it, but he knew the two countries both had moved. It is so. They are not simply exchanging their often still very different positions but, it seems, they are listening hard. This may mean that some problems will not be resolved or agreed on -- not soon, at any rate. Living with differences, peacefully and respectfully, while trying hard to resolve them, has its own value.