PRESIDENT Bush envisions December's ``floating summit'' as an occasion when he and Mikhail Gorbachev can sit in deck chairs, feet up, and discuss the great affairs of the day. The folksiness, of course, is deceiving. Even with informality built in, this meeting will have a tension provided by the swiftly changing world around the two leaders. Mr. Bush says he proposed the meeting - reversing an earlier aversion to unstructured summits - because he wanted to get the word on Soviet attitudes toward events in Eastern Europe right from Mr. Gorbachev's mouth, in case he was missing something. He also wants to outmaneuver critics who say he hasn't done much to emphasize US interest in the reforms sweeping through Poland, Hungary, and the Soviet Union itself.
The December meeting indicates, too, that Bush is aligned with Secretary of State James Baker's position that Washington should do what it can, quickly, to support the thrust of perestroika. That's where he should be.
Warnings sent up in the wake of the summit announcement can't be ignored. Students of summitry quickly recalled the near-disaster in Reykjavik, Iceland, in 1986 when Gorbachev sprang a sweeping arms control proposal on an unwary President Reagan. The Western alliance shuddered. Bush says he expects no such surprises aboard the warships off Malta, since arms control decisions are reserved for the full-blown summit scheduled for next spring or early summer.
As an added caution, the president presumably has been in contact with European allies and has plans to brief them at the end of his Dec. 2-3 talks with Gorbachev.
One goal is to let the two leaders get better acquainted. The personal aspects of diplomacy have their place, and their limits. Historians recall, for instance, Nikita Khrushchev's misreading of John F. Kennedy at their first meeting, which may have led to Soviet miscalculations in Cuba.
Still, it makes sense for Bush and Gorbachev to have the best possible understanding of each other's interests and goals as reform overhauls Eastern Europe.
Nothing startling is likely from this ``nonsummit summit.'' It's purpose, after all, is to avert the startling in superpower relations.