Vilamoura, Portugal — The Western alliance is likely to reduce the number of tactical, or battlefield, atomic warheads in Europe. This could be the significant story from the NATO nuclear planning group concluding in Portugal Wednesday.
Over the long term, such a move could be more significant in avoiding nuclear war than whether the United States offers a nuclear-arms ''interim solution'' at negotiations now under way with the Soviets, or whether NATO in fact deploys Pershing II and cruise missiles as planned.
Recently, officials in the Pentagon and at NATO headquarters have questioned the usefulness of these smaller nuclear rockets and artillery shells, some 5,000 to 6,000 of which are positioned and stored in Western Europe. Many of these are old and unreliable, yet vulnerable to Warsaw Pact attack. There is also increasing concern that they will become the target of nuclear protesters.
The Reagan administration budget contains more money for producing newer versions of such weapons. But in recent congressional testimony, the NATO Commander, Gen. Bernard R. Rogers Jr., warned that nuclear war could not be contained in Europe and would quickly escalate to a strategic, or intercontinental, exchange between the two superpowers' full nuclear arsenal.
Such weapons are relatively small compared with intercontinental ballistic missiles, but many are several times larger than those exploded over Japan in World War II.
Within NATO, the so-called ''high-level group'' of experts is expected to recommend later this year that the number of tactical nuclear weapons (generally with a range of less than 100 miles) be cut back.
''We ought not to retain weapons in the inventory that are not militarily useful,'' said a high-ranking official with this group.
As with intermediate-range nuclear forces, the Americans seem to be taking a more hawkish position on tactical nuclear weapons than their European counterparts or concerned members of Congress. US lawmakers last year refused to appropriate money for new nuclear artillery shells, but the proposed Pentagon budget for the coming year again includes this request.
NATO's interparliamentary assembly reportedly will soon recommend that such weapons be reduced, and Sen. Joseph R. Biden Jr. (D) of Delaware (who heads the group) is asking other senators to support this effort.
As General Rogers told Congress, the US at present has a numerical advantage over the Soviet Union in short-range nuclear weapons, one of the relatively few weapons in which NATO has a clear edge. General Rogers advocates a new doctrine whereby NATO would oppose attacking forces behind the lines of engagement with precision-guided conventional weapons, rather than resort to nuclear arms.
''We have mortgaged our defense to the nuclear response,'' General Rogers told Congress earlier this month. ''We face the serious risk of having no recourse other than the early first use of nuclear weapons to defend the alliance.''
But to correct this situation requires West European countries to spend more on conventional forces. General Rogers says the 4 percent annual increase in defense spending necessary to meet this goal would average just $23 for each person living in a NATO country. So far, however, European governments, in the midst of recession, have not agreed to spend such sums.
''What remains to be established is whether the willingness to pay the bills is there,'' said a senior US official.
As part of its plan to deploy 572 Pershing II and cruise missiles beginning late this year, NATO already has agreed to reduce older theater nuclear weapons by an equal amount. Sources here say the nuclear-armed Nike Hercules air defense weapons are sure to be phased out as well.
As pressure builds on both sides of the Atlantic to prevent nuclear war, it seems likely that even more nuclear warheads will be removed from European soil.