IT WAS at the least a civil summit. Whatever differences were expressed in their long sessions alone, in public President Reagan and General Secretary Gorbachev were at pains to display restraint and amiability. A hint of frustration seemed to touch Mr. Gorbachev's remarks at his press conference yesterday. The president acknowledged last night to Congress that he had paid Mr. Gorbachev "the tribute of candor." Yet on the surface, cordiality and forbearance reigned.

There is always the risk, in these summit extravaganzas, that the chemistry will go sour or that differences will widen into misunderstanding or worse. By this standard it would have been enough for the president to come home cloaked in an aura of relief that relations had gotten no worse. In fact, both leaders said that something more positive was achieved in the way of mutual understanding and that a political impulse was given to arms control. That two more summits are in the offing is reassuring. Much can be said for a subdued and steady approach to Soviet-American relations, especially when the gap in formal positions and in leaders' perspectives is so broad.

Still, the relative thinness of tangible results is notable. The exchanges and humanitarian relief and other items were something, but the summit did not produce agreement even on the full list of lesser bilateral accords that had earlier been described as fit for Geneva sanction. Nor was there public sign of any decision on the large arms control issues or on the regional disputes that lie at the heart of Soviet-American rivalry.

For Mr. Gorbachev, one can guess that his failure to stop the American Strategic Defense Initiative, which the Kremlin had characterized as his chief summit mission, had something to do with his readiness to paint as successes the less tangible atmospheric modifications. At his press conference he insisted that slamming the door on SDI was the continuing Soviet condition for "radical" cutbacks in offensive arms. Nonetheless, the final joint statement recorded his agreement to seek "early progress" in "areas where there is common ground." The "areas" named exclude the Soviet priority of space arms but include the American priorities of deep cuts in offensive strategic arms and an interim accord on missiles in Europe.

The secretary of defense and some others had urged Mr. Reagan not to trade away SDI or to extend the controls of SALT II. Mr. Reagan evidently didn't. Nonetheless it seems premature to conclude that "Weinberger won" on the Washington arms control battlefield or, for that matter, that the perfunctory language in the joint statement on regional issues means there are no chances fr restraint there either. The deepening of consultation could turn out to be important.

It would have been useful if the two men had worked out the framework for arms control that was being talked about in the administration before the president left Washington. But for them to come out of their first summit talking, and talking civilly, makes Geneva an accomplishment. For Ronald Reagan, who neither wobbled nor froze (as the various anxious feared), it was a personal accomplishment too.