NATO planners eager to know: Will US base MX on land or at sea?

The story of the April 7-8 NATO Nuclear Planning Group (NPG) meeting in Bonn --the public story, at least -- is that of the shoe that never dropped. The most urgent question in inner NATO affairs was never mentioned in press briefings -- apparently because the issue is still deemed too hot for public discussion.

The question is this: Will the US ultimately decide to base its projected MX missile on submarines -- and, if so, will NATO then also decide to put its planned new nuclear missiles at sea rather than on land?

The issue is a crucial one for Northern Europe, which faces extensive public opposition to the new cruise and Pershing II missiles planned for late 1983 deployment on land.

As a preview of what is expected to be a long, hot summer, some 12,000 to 20, 000 demonstrators kicked off the season in Bonn with a peaceful antinuclear protest just before the opening of the NPG meeting. And posters all over Bonn advertised an anti-NATO nuclear evening (sponsored by the youth wing of West German Chancellor Helmut Schmidt's Social Democratic Party) featuring, among other speakers, a correspondent for the Soviet news agency Novosti.

Even stronger public opposition in the Netherlands and Belgium has prevented these governments from getting parliamentary approval for agreed new nuclear deployments on their soil. the ban-the-bomb movement is reviving in Britain as well. And there is every expectation that nuclear opposition will grow in Western Europe.

It is therefore of much more than academic interest to Western Europe how the Reagan administration eventually sorts out its own strategic missile systems. To Western Europeans the logic is clear. If the US rejects land basing of the MX missile, it will be for two reasons:

* Environmentalist opposition from local inhabitants of the sparsely populated American desert where any land-based MX would be deployed.

* An expert assessment that the marginally greater accuracy of the land-based MX over the sea-based version would not be a critical factor.

These same considerations would apply doubly to the deployment of any new landbased missiles in a densely populated Europe that is much closer geographically to the Soviet Union and therefore has less need of the pinpoint accuracy required of today's intercontinental missiles.

But in December 1979, NATO made the crucial decision to deploy 572 cruise and Pershing II missiles in Europe by 1983, if arms-control talks did not lead to agreed missile ceilings before then.

Now, one knowledgeable West German says flatly, "If Reagan deploys the MX in a sea-based mode, you can forget the 1979 decision. The whole concept would have to be changed."

It is not yet known what the US reaction to such European reasoning will be. There are counterarguments. Clearly NATO submarines in the Baltic and Mediterranean seas would not be anywhere near as safe from potential Soviet attack as the American offshore subs that are being mentioned for a seagoing MX. And a few more American NATO-assigned subs in the North Atlantic might not have the same deterrent effect on the European continent as a commitment by Western European populations to station new landbased missiles on their own soil.

Still, the US could hardly require its European allies to do what Washington itself was unwilling to do politically.

And the West European governments --which are convinced of the need for new deployments to offset the new Soviet nuclear medium-range superiority to Europe -- could sell this necessity to their publics much more easily if the weapons in question were sea based rather than land based.

In NATO's view the Soviet superiority in "Eurostrategic" (European-based medium-range) weapons dates from the late 1970s deployment of the Soviet SS-20 mobile missile.

Official NATO statistics now place the number of deployed triple warhead SS- 20s at 200 (out of a projected 300 by the mid-1980s), with two-thirds of these aimed at Western Europe, one-third at China.NATO has no missile of comparable range; even the planned single warhead cruises and Pershing IIS planned for mid-'80s deployment will depend on flexibility and accuracy rather than range for effect.

In a public update of other figures.NATO's director for nuclear planning, David Martin, told reporters that the 1,000 short-range NATO nuclear warheads to be retired in connection with the December 1979 NATO modernization decision have already been withdrawn. This leaves some 6,000 short-range NATO nuclear warheads in place until 1983, when an equivalent number of the old short-range warheads will be retired as the new medium-range ones come on line.

Other business taken up by the super-secret NPG meeting in Bonn included the still fluid American policy on arms-control negotiations and the perpetual American wish for higher European defense spending.

At the NPG meeting the US repeated the promise it gave the anxious Europeans in Brussels March 31 at the meeting of the NATO special consultative group -- to resume arms-control negotiations on eurostategic weapons with the Soviet Union. Washington still has not given its allies any fixed date for these negotiations, however.

Chancellor Schmidt has publicly been plumping for summer, but American sources doubt that it would be before fall. A final date is not expected to be set in any case before Mr. Schmidths visit to Washington at the end of May. And both the Americans and West Germans appreciate the value of leaving the timing open until Soviet actions in Poland become clearer.

On the issue of defense spending US Defense Secretary Caspar Weinberger again asked his European colleagues for some reciprocal sacrifice to match the huge American hikes in defense budgeting. Both American and West German sources report that the atmosphere is very different from the budget squabbles of the Carter era, however. The spirit is said to be much more one of facing common urgent needs in a money-tight period of recession and trying to wrestle out common priorities.