Making the most of a captive audience at the annual meeting of the American Society of Newspapers Editors, Defense Secretary Caspar Weinberger asked the people who decide what's news to help clear up "misconceptions" about President Reagan's Strategic Defense Initiative (a k a "Star Wars").

Very well, let's begin with basics. The latest high technology is the name of the Pentagon game. The strategists, the field commanders, the procurement officers all play it, all the time, with willing collaborators: scientists whose zest for research and technological breakthroughs is more than matched by their appetite for the wherewithal to pay for it.

There was, then, a live constituency ready to welcome the president's celebrated announcement of his plans for a "comprehensive and intensive effort to define a long-term research and development program" to develop a nuclear defense system based at least partly in space. All but lost in transmission of what sounded like something stunningly new was any sense that all the president was doing was giving a considerable boost to R&D efforts that had been under way for years.

Now, it's true that the president's SDI budget request calls for $26 billion over the next five years, which would be an increase by a "factor of two," according to experts, over the spending rate previously contemplated. But even at this spending rate, the president was careful two years ago to speak in speculative, futuristic, turn-of-the-century terms. Yet that, too, has been lost in transmission. As the administration turns up the volume of its sales pitch, it also adds variety in a way that makes today's case for SDI strangely at odds with the original vision.

If the nation's editors are to help clear up misconceptions, then they're going to require help in return. First impressions do matter. And the first impression conveyed to the American public, Congress and the European allies -- not to mention the Soviets -- was that the United States was on to something genuinely new. The boundary lines between R&D and the next step, testing -- to be followed by deployment -- were thoroughly blurred.

Within a week after his March 1983 speech, the president elaborated in an interview: If the United States cracked the case and came up with a workable, leakproof defense against nuclear weapons, a future president could "offer it" -- share the technological secrets, that is -- to the Soviets. Then everybody would be protected by a nuclear "bubble" and, presto- chango, we would have a world free of the threat of nuclear war.

The first result was a raging debate among scientists, with enough weight on the side of the skeptics to raise serious questions about whether any foolproof system could be achieved in an foreseeable future, and never mind whether the United States could conclusively steal a march on the Soviets so decisively that it could afford to pass the technology along. A lot of thoughtful people found it hard to conceive of a state of relations between the superpower adversaries that would make that possible.

So we don't hear any more about that. Rather, we hear the opposite: that the Soviets are stealing a march on us, that they are well ahead in their research into lasers and particle beams and more conventional antimissile defenses. That's now become the main argument for why the United States must redouble its effort: to catch up.

It's not a bad argument. Not even the uneasy Europeans oppose research, the more so since they are being offered something in the way of hush money: a piece of the research action by competitive bidding. But the Europeans, led most vocally by British Prime Minister Margaret Thatcher but also by the quieter and earlier efforts of the French, are a lot more explicit about those boundaries between research, testing and deployment.

They know the momentum of these matters, the high cost of the early development, and the disinclination to raise questions along the way about sending good money after bad. So the Europeans, as well as a good many Americans, are not entirely reassured by the administration's vision of a gradual, safe transition from a strategy of deterrence by the threat of retaliation to a strategy of nuclear defense.

And not the least of the reasons for this disquiet has to do with "misconception" of the administration's own making: a confusion between the poetry of nuclear disarmament and the prosaic business of research looking to a state of the art and of the world that nobody now foresees.