IT WAS a more worn and subdued looking Mikhail Gorbachev whom George Bush greeted at the White House yesterday. It was not hard to imagine that his and his country's mounting cares had taken the edge off the high energy and confidence he had earlier displayed. The loss of empire, the challenge to Mr. Gorbachev's political leadership and the general erosion verging on incipient disintegration in the Soviet Union provided a sober backdrop to his evident purpose to apply some order to events otherwise apparently spinning out of control. His reception on the streets of Washington was considerably more friendly than what he gets these days in Moscow.

President Bush received his guest with personal grace and with an unprovocative but clear statement of the American interest in a deepening of the democratic trends within the Soviet Union and -- a matter increasingly seen to be related to the first -- a consolidation of the changes taking place in the international arena. For the United States, the requirement is to show steadiness and patience in the face of opportunities that are coming within reach but are not yet there. These opportunities center on consummating a post-Cold War European settlement, involving security, political consultation and economic exchange -- a settlement that, as Mr. Bush said in his greeting, satisfies all parties in Europe and threatens none.

It is quite likely that this is too grand a task to be achieved at one summit. It indicates the common aspiration, however, that the two leaders assigned overnight homework to their aides. Progress in important though not exactly world-shaking arms control issues had already been ensured in this summit. Any further work would perhaps best be measured in terms of momentum imparted and new formulas explored on the basic European issue.

A Soviet-American summit inevitably magnetizes the hopes and pleas of many other countries and many causes. This one is no exception, but it has its own quality. Because of contributions made by Mr. Gorbachev and Ronald Reagan, there is no sense of a fundamental war-or-peace choice hovering over this summit. That's been ''done.'' Rather, the common emphasis is on clearing away the political and intellectual wreckage of the Cold War and getting on with the life that comes after.