FOR the past five years, the NATO allies have aimed - with limited success - at a target of 3 percent real growth in defense expenditures. When they set the goal in 1978, most allies thought it was a difficult but not impossible objective to average over five years. This, however, was before the 1978-79 oil price increases and the consequent recession, which brought economic growth in most NATO countries to a grinding halt.
Now that the 3 percent goal has expired, the allies are seeking a suitable replacement. The question is on the agenda for the annual end-of-year meetings of NATO defense and foreign ministers this week.
Meanwhile, the allied failure to meet the goal has become the principal focus for congressional criticism of allied defense efforts. For some members of Congress, the 3 percent formula has become a litmus test of European commitment to the alliance - a test which, in their view, the allies have so far failed.
In recent years, NATO's supreme allied commander, US Gen. Bernard Rogers, has argued that NATO countries need to increase defense spending by at least 4 percent a year to reduce reliance on the early use of nuclear weapons to blunt a Warsaw Pact offensive. But there is no way the allies, climbing slowly out of recession, will sign on to a ''4 percent solution.''
Many NATO experts believe that it would be more constructive to focus allied objectives primarily on output goals - what the allies get for their money - than on a simplistic input goal like the 3 percent objective. NATO's new secretary-general, Lord Carrington, the former British foreign secretary, has suggested that the European allies concentrate on improving NATO's infrastructure, such things as airfields and control facilities.
NATO professionals recognize that the failure of the allies to meet the 3 percent goal has been a serious political liability for the alliance with US public opinion. The failure contributed to the substantial congressional support for Sen. Sam Nunn's proposal this year to cut US troops in Europe unless the allies met the 3 percent objective in the future or made specific improvements in their defense efforts. Most experts argue that such ''punitive'' legislation, if passed, would not have the desired effect in Europe. But simply saying ''goodbye'' to the 3 percent solution without providing some prominent new goals might raise a considerable furor in the next Congress.
If the allies conclude that some input goal must be retained, they might consider making the objective more relevant to fluctuating economic circumstances in NATO countries than was the 3 percent solution. For example, NATO could agree on a real growth plus one formula for future defense spending, linking the defense spending objective to economic performance, and therefore to available government assets in NATO countries.
A ''real growth plus one'' formula would retain the incentive for growth in defense expenditures, but in a way more directly related to allied economic fortunes. For example, under such an approach, if West Germany were to realize real economic growth of 1.5 percent in 1985, the following year the government in Bonn would budget at least 2.5 percent real growth for West German defense spending in 1987. This approach would at least take into account the direct relationship between economic performance and the relative ability of each ally to increase its contribution to the alliance. And, combined with a variety of ''output'' objectives, such as those proposed by Lord Carrington, the approach could chart a more realistic course toward decreased reliance on nuclear weapons.
Debates over sharing the NATO burden have been part and parcel of transatlantic relations since the 1950s. They will remain a prominent feature of the alliance landscape for as long as NATO allies are faced with competing demands for limited resources - in other words, for the indefinite future. The challenge for the allies today is to frame the issue in such a way that countries are encouraged to fund required improvements to sustain deterrence, yet to do so in a way that protects the fabric of alliance cohesion from political and economic frictions inherent in burden-sharing relationships.