THE SUGGESTION of some of the tapes is that the Soviet defense network misidentified the Korean Boeing 747; the thought was that it was a U.S. Air Force RC135, a military reconnaissance version of the smaller and older 707 that, American officials acknowledge, flies regularly off Soviet shores. The Soviet air defense commander offered the misidentification theory yesterday. Does it plausibly explain shooting down the Korean airliner?

A mixture of confusion and incompetence--compounded by the Soviet Union's paranoia and the rigidity of its air defense instructions--is conceivable. But it does not constitute anything near a full or satisfactory explanation. Why were the differences between a 747 and 707 not noted? How were the Korean markings avoided? Why not let dawn resolve the doubt? Why shoot to kill?

And once Western alarms had established the civilian character of the loss, why not let others join the search? Why, still, no actual acknowledgment that a Soviet hand fired the missile that destroyed the plane and 269 lives? Why such a stingy expression of regret? Why a fake and vicious counterstory of a Korean and American espionage mission?

Perhaps more information will come into the public domain. In the meantime, President Reagan's handling of this affair deserves to be commended. His basic constituency, including the part of it lodged in the bureaucracy, sees in the incident not simply a proof of its and Mr. Reagan's long-held convictions about the Soviet Union. It sees as well an occasion to pull the president back from the way he has gone about trying to make agreements with the Soviet Union over the last year.

Convinced as many of them are that Mr. Reagan is an unreconstructed hardliner, the president's critics on the left often show only the slightest comprehension of the heat he has generated among his natural political environment on the right. It is a tribute to Mr. Reagan that he seems to have acted according to his best judgment in this episode rather than in reaction to political pressures. He has been acting presidential.

Mr. Reagan is to make known his response to the Soviet Union this evening. The word is that he will suggest a range of measures designed to call the Soviet Union to public account and, in as broad international company as possible, to take steps in the area of civilian air travel and safety. The more he shows himself to be acting in a presidential rather than a partisan or ideological mode, the better the chance that his policy will work.