PRESIDENT REAGAN'S proposal of last March to study shooting down Soviet missiles in space anticipated a time and a technology far in the future. But another kind of "space war" is becoming possible in the here and now: weapons to shoot down the satellites on which both great powers increasingly depend for communication and intelligence. The Soviet Union already has launched (non-nuclear) weapons meant to kill low-orbiting American satellites. The United States is ready to flight-test its own first satellite killers. A down payment of $19 million, on a program that could yet cost billions, is due to be voted on in the House this week.

It is a serious business. One side's possession of effective anti-satellite weapons could theoretically let it "blind" the other--deprive it of the means to control its own strategic forces and detect its foe's. Just the fear that one side might attempt such a blinding strike in a crisis could force decisions of irreversible consequence. Yet Moscow and Washington have been unable to take the risk in hand.

Carter-era negotiations tripped over verification, among other things. Anti-satellite weapons, it turns out, are small and light and can be launched as easily and quickly as the satellites they are aimed at. A relative handful of them could threaten a major share of a great power's missile-detecting or -guiding satellite capacity, making reliable verification essential.

The Carter administration had hoped that a discreet brandishing of American technological capacity, combined with active negotiations, would induce Moscow to rein in its own anti-satellite work. This policy did not fare well, and now the Reagan administration is heading toward deployment of the first American satellite killers. At the same time, it hangs back from resuming negotiations.

The new American weapons are considered to be substantially superior to the Soviet weapons already in orbit. We should proceed with caution in deploying them. Meanwhile, a new approach to negotiations should be devised. Reagan officials say talks should not resume until the United States is "ready with verifiable proposals that will enhance national security." Why is the administration, in its third year, not ready? If it is too hard now to negotiate limits on deployment, why not try to limit tests? In this branch of weaponry as in others, the administration has yet to find an effective, confidence-inspiring balance of arms building and arms control.