On second thought, West European governments don't like President Reagan's ''star wars'' defense idea any better than they did at first blush. Their initial recoil last month to Mr. Reagan's sudden setting of a goal of a comprehensive American (laser) defense against Soviet missiles was political.
* According to European diplomats and defense officials, they felt that Washington was once again turning the West's two-decades-old defense consensus on its ear - without consulting or even warning its allies.
* They thought that the timing of such an announcement was unfortunate. At this sensitive point in the current Euromissile arms-control negotiations, they feared it would only help convince the Soviets (and West European public opinion) that Washington was not serious about arms control - that it was in fact seeking not a nuclear balance, but superiority over Moscow.
* They were disturbed by Secretary of Defense Caspar Weinberger's assertion that working on a laser antimissile system would not violate the 1972 antiballistic missile treaty. They viewed this as coming close to a unilateral United States dumping of that treaty's ban on ''development'' of comprehensive antiballistic missile defenses.
By now, the West European governments have had time to go beyond their instinctive political reactions and analyze the pure security implications of any ''star wars'' military regime. And they find this security analysis no more reassuring.
For the British and French, such a regime would make their present nuclear weapons useless and deprive them of the deterrence value of possessing those weapons. For West Germans, as for all West Europeans, such a regime would essentially leave them defenseless against the Soviet Union. It would repeat the hostage-Europe situation of the 1950s - but this time they would be facing a far more powerful Soviet adversary.
The reasons a laser defense for the US (and the Soviet Union) would paradoxically leave Western Europe less defended lie in the peculiar logic of the nuclear age.
Ironically, ever since 1945 deterrence, or war prevention, has rested on the very horror of nuclear weapons and the absence of any conceivable defense against them. In the past two decades, each superpower has had the capacity to destroy civilized life in the attacking nation within half an hour.
Under these circumstances there has been a standoff. Both superpowers have been extremely cautious about confronting each other where their stakes are highest - in Europe. Under the compulsion of this ''balance of terror'' Europe has by now enjoyed its longest period of peace in this century.
Under these circumstances, too, any move toward developing a comprehensive defense against missiles by either superpower has been viewed by the other superpower as a threatening attempt to gain superiority. That is, deterrence holds so long as both sides are equally vulnerable. Such restraint could vanish, however, if one side achieved superiority by making itself invulnerable while still keeping its adversary vulnerable.
This reasoning induced both sides to negotiate the 1972 treaty banning development of any comprehensive antiballistic missile defense. (At the time, in any case, no technology was on the horizon, as lasers are today, that might promise such a defense.)
This reasoning also caused various American hawks to view Moscow in recent years as striving for such an unacceptable destabilizing defense in its civil defense and antisatellite research programs in particular.
Now that the US is seeking an antimissile defense, however, the shoe is on the other foot. American hawks are applauding the effort, while Soviet hawks are in turn accusing Washington of striving for a destabilizing defense.
The clearest idea of where this leaves Europe is perhaps best gained by looking back at the 1950s and early 1960s, before Washington and Moscow ushered in the full balance of terror by developing intercontinental missiles.
At that time, the US still had a clear superiority over its rival in nuclear offensive weapons through its strategic bombers. In any conflict it could have destroyed Moscow without fearing that the Soviets would destroy Washington in return.
Moscow balanced this off, however, by holding America's allies in Western Europe hostage. From halfway around the world the US could not reliably defend Western Europe as such. Soviet conventional superiority in Europe, and then the medium-range nuclear missiles Moscow began deploying in 1959, meant that the Soviet Union could always destroy Western Europe in retaliation for any American attack.
Conversely, any Soviet attack on Western Europe could have been met by American ''massive retaliation'' against the Soviets.
If laser defenses are now developed that could give the US and the Soviet Union secure defenses against each other - a large ''if,'' since many scientists doubt the technical feasibility - Europe would essentially revert to this 1950s situation. The differences would be, however, that given the superpower parity that now exists, the US could not protect Europe now as it did then by threatening massive retaliation against the Soviet Union. And the medium-range nuclear superiority that the Soviet Union has developed in the past five years in the European theater would be far more threatening to Western Europe now.
The reason for this is that laser defenses - as so far conceptualized - would intercept intercontinental ballistic missiles at the apex of their trajectory, in the stratosphere, or at the edge of inner space. ''Euromissiles'' don't go that high and would not be subject to laser interception. (Nor, in fact, would ''depressed-trajectory'' intercontinental missiles - this is one reason for skepticism about ever developing a 100 percent reliable laser defense.)
There are thus four basic scenarios of what a laser defense regime would mean for Europe that are being analyzed here. All except the fourth (and most unlikely) one are alarming.
The first scenario is nicknamed here ''fortress America.'' In it, the US would have both defensive and offensive weapons, while the Soviet Union would have only offensive weapons. The laser system would defend the US against Soviet intercontinental missiles. At the same time, Washington would maintain its own offensive intercontinental missiles to maintain West European security - that is , to threaten retaliation against the Soviet Union for any attack on Western Europe.
Once such American 1950s-style nuclear superiority over the Soviet Union was established, Western Europe would enjoy full protection. The problem, however, lies in getting from here to there. It would require some years for the US to build such a dense defense system, even after it deveoped the appropriate technology in the late 1990s, say. And that transition period would be an extremely dangerous one. A desperate Moscow, foreseeing the return of American superiority, might see its last chance in preventing this in a preemptive attack on the vulnerable American satellites that would direct the laser system.
In the second (improbable) scenario, the US would reassure the Soviet Union by dismantling its own offensive weapons as it built its defensive mantle. This might solve the problem as far as the superpowers are concerned. It would, however, leave Western Europe at the mercy of the Soviet Union: superior theater conventional and nuclear forces, since the US would then pose no ''deterrent'' threat of retaliation on the Soviet Union for any Soviet attack on Western Europe.
In the third scenario - ''fortress America plus fortress Russia'' - both superpowers would develop laser defenses simultaneously. In such a circumstance, Western Europe would again be naked, since the US could no longer provide Western Europe's ultimate guarantee by threatening retaliation on the Soviet Union.
In the fourth (most improbable) scenario, laser technology would be developed to the point of defending against Euromissiles as well as against intercontinental missiles. Europe, too, would then be protected against ''long-range theater'' ballistic missiles. It would not, however, be defended against shorter-range ballistic or cruise missiles, which both NATO and the Warsaw Pact are expected to deploy in the next few years. The result would be a standoff of the same sort that exists today.