DOES President Reagan really believe in ''Star Wars''? You find yourself asking that question while listening to Defense Secretary Caspar Weinberger explain it at the National Press Club. It was a sophisticated audience of about 250. The questions were mostly or all doubtful. We came away wondering.
President Reagan introduced ''Star Wars'' unexpectedly in a nationwide TV speech March 23, 1983, in which he made the extraordinary announcement, ''I've reached a decision which offers a new hope for our children in the 21st century. . . . This subject involves the most basic duty that any president and any people share, the duty to protect and strengthen the peace.''
The technical name for it is ''Strategic Defense Program.'' The irreverent immediately dubbed it ''Star Wars.'' Up till now, Mr. Reagan said, we had depended for peace on the threat of retaliation if attacked. But what if we created a kind of permanent protective system or shield over us - the knowledge ''that we could intercept and destroy strategic ballistic missiles before they reached our own soil or that of our allies''?
Mr. Reagan was cautious about this ''new hope for our children'': He said, ''I know this is a formidable technical task, one that may not be accomplished before the end of this century.'' The public found it hard to visualize. Mr. Reagan seemed to be proposing a kind of shield overhead, an astrodome of defense. People looked at each other. Said the dubious Union of Concerned Scientists, one has to believe ''in a defense of stupefying complexity under the total control of a computer program whose proportions defy description, and whose performance will remain a deep mystery.'' It could never be tested, they noted, until the moment of actual use.
It should be remembered that nuclear defense can't be just partly or even 99 percent effective; if it is not absolute, it loses its meaning. Mr. Reagan was challenged on the subject by reporters at a press conference March 25, 1983. Rival leaders, he said, sit across a table with cocked guns. ''Now,'' he said, he would ask ''the same scientists who gave us this kind of destructive power to turn their talent to neutralizing them.''
Critics of Mr. Reagan ask if he is using ''Star Wars'' to counter the nuclear freeze groups who want less money spent on defense. Richard Halloran, a defense correspondent of the New York Times, noted in January:
''Over the last 18 months President Reagan has clearly stepped into the front ranks of those American Presidents who, since World War II, have been willing to employ military force as an instrument of national policy.'' The reporter says, ''He has put marines in Lebanon, mounted a show of force againct Libya, ordered the invasion of Grenada, sent ships and soldiers to Central America, and authorized covert use of mines off Nicaragua.'' In contrast to Presidents Ford and Carter, Halloran thinks Mr. Reagan ''represents a return to a reliance on military power to achieve political objectives.'' He thinks Reagan has shown himself to be ''bolder than his generals.''
I looked down from the Press Club gallery trying to weigh the words of the earnest, fast-talking defense secretary who knows the President so well. Did he believe that a successful Strategic Defense Program could be developed? Mr. Weinberger said, ''It must be tried.'' ''Perhaps it won't work,'' he said; but remember, learned technicians said a strategic missile that could cross the Atlantic and hit a target in Europe was ''impossible.'' How can we know what can be done?
Questions from the audience were handed up to the head table. They all spelled doubt. Mr. Weinberger remained earnest, but courteous. He criticized presidential aspirant Walter F. Mondale by name, for pooh-poohing ''Star Wars'' as something that would ''open the heavens for warfare.'' Didn't he know the Russians had been trying that since 1967?
We came away wondering. President Reagan argues that his ''Strategic Defense Program'' shows him as peace-loving. But is it practical? An indirect commentary came on the Weinberger speech itself, which was carefully prepared and presented in a blaze of TV camera crews. But it received little press attention. Everybody yearns for the goal, but what is the next step? One comes away hoping that when the US elections are over, President Reagan, a new Democratic leader, or both will meet General Secretary Konstantin Chernenko, either here or in Moscow, to talk things over.