By postponing the Feb. 11-13 summit in Moscow, President Bush has taken a step that is necessary but regrettable.

It is necessary because of unexpected snags in working out some technical details of the new treaty that was to be the centerpiece of the summit - the treaty reducing long-range nuclear missiles by one-third.It is regrettable because of the risks involved in the delay even though the postponement of the summit sends Mikhail Gorbachev a pointed and pertinent message. The message, of course, is that widening repression in the Baltics may cost the Soviet leader badly needed support from the West.

One risk is that Gorbachev may consider the delay in the summit such an affront that he will start backing away from Soviet support for the allied war against Iraq.

Another risk is that the U.S. move could further erode Gorbachev's ability to stave off his own Soviet hard-liners who would like to revive the Cold War.

Still another risk is that timing of the decision to delay the summit makes it look as if the Persian Gulf war is keeping President Bush a prisoner in the White House, even though he insisted that would never happen.

Meanwhile, this episode holds a couple of important lessons for Americans. One lesson is that there are sharp limits to how much Washington can influence internal developments in the Soviet Union. Another is that the makers of U.S. foreign policy had better start preparing a fall-back position in case there's a change in the leadership of the Kremlin or the present leadership abandons its efforts at reform.

In any event, the timing of the Moscow summit is not nearly as important as making sure it is eventually held. It's essential to maintain the momentum behind further arms control agreements, which can do more to make the world safer than anything that seems likely to happen in either the Baltics or the Persian Gulf.