BEFORE THIS thing gets completely out of hand, it seems important to us to stamp out a false allegation, not to mention a base canard, concerning President Carter and that cageful of unsinkable balloons. You remember the ones -- the gala balloons nested by the ceiling of Madison Square Garden on acceptance-speech night that were supposed to float gracefully down upon the celebrants . . . and wouldn't. The base-canard part is the theory, at once espoused by practically everyone, that this was just more evidence of Jimmy Carter's inability to make things happen or to make them happen right. Even the balloons, the thinking went, we're saying: Hell, no, we won't go.

Not fair. Not even true. No, there is an entirely different principle at work here, and it has nothing to do with Jimmy Carter's resume. What happened Thursday night was that a law of nature was violated by the Democrats, or an attempt was made, anyway; and nature simply resisted, fought back. We explained in this space a few weeks ago the fundamental axiom of political conventions: Democratic balloons float up , Republican balloons float down . This is the way God intended it to be. It has always been this way. Our curiosity was piqued buy the fact itself and we tried to figure out what in science might account for the phenomenon, but had to conclude more research-evidence was required.

This was before either of the 1980 conventions had occurred. Now we do have more evidence. All week long the Democrats in the Garden floated balloons -- green ones and blue ones and clear ones -- upward (just as the Republicans, in Detroit, being at one with nature, had floated their balloons downward in accord with the Law). But on Thursday night the Democrats tried this other thing: they moved to the right -- they tried a downward Republican float . And it didn't work. The balloons wouldn't release, or vast numbers of them wouldn't. Sen. Kennedy would be a fool not to seize on this portent of things to come. The Democrats are not going to be able to mimic the other party, as some of them hope to. They are going to have stay Democrats. It is nature's will.