Washington — The new-old debate over US troop levels in Europe is one that will not go away. In fact, despite the narrow defeat in the Senate last week of an amendment that could have sharply reduced Uncle Sam's NATO presence, the relative importance of Western Europe to United States strategic interests inevitably will decrease.
This is the feeling of many civilian defense experts as well as those in uniform. It is hinted at in the Reagan administration's national-security actions and pronouncements. It is the logical response to increased Soviet military activity in the Pacific and elsewhere, as well as to the realization that US military resources are finite.
The vigorous discussion over the role of US forces in the world today can loosely be called ''maritime strategy vs. coalition defense'' (which happens to be the title of a new book by former Pentagon official Robert Komer.)
The argument centers on whether the US should be concentrating as much as it is on a traditional post-World War II role of protecting the European landmass against Soviet invasion, or whether these days it has more pressing commitments around the world - like the Persian Gulf and Latin America.
The Reagan administration does not want to be seen as backing down in Europe. But White House officials frequently note that Ronald Reagan is the first ''Pacific President,'' that he does have a special concern for such things as the steady buildup of the Soviet ''bluewater Navy'' in the Pacific - including the takeover of former US naval facilities in Vietnam.
This relative downplaying of Europe - which dates back to efforts by former US Sen. Mike Mansfield to pull back American troops from Europe - has to do with several other important factors.
It generally is agreed that nuclear war - while it would be devastating - is very unlikely to occur. Massive conventional war in Europe is only slightly more likely, and NATO officials themselves reported last week that the size and fighting capability of the Warsaw Pact probably has been overstated.
When non-NATO French and Spanish forces are included in the balance, and when certain intangible but very important factors (training, troop leadership, morale, alliance cohesiveness) are taken into account, the Soviet threat does not loom quite as large.
At the same time, recent studies by and for the US military services (especially the Army) conclude that third-world insurgency, regional conflict, and perhaps terrorist operations will become the more likely threats. The current US rebuilding of special-forces units, jungle- and desert-training efforts, and counterinsurgency and antiterrorist skills is a response to these threats.
That generation of military officers now assuming operational command of battalions, ships, and squadrons served its formative years in Vietnam.
There remains bitterness over that experience and hesitancy to fight again without much more public support. But many of these officers still feel that the threat in Southeast Asia needed a US reponse and that the defeat was not military but political. And these same officers are moving into senior staff positions, where they are gaining increased policymaking power.
Within the Pentagon itself, the most active of the three service secretaries is Navy Secretary John Lehman, a vigorous and forceful proponent of maritime superiority and a naval strategy that seeks to engage the Soviet Union all over the globe if necessary.
Despite the criticism of military reformers and budget-cutters, Secretary Lehman has succeeded in winning the 600-ship Navy that is the centerpiece of the Reagan defense buildup. And most of these ships are surface combatants and submarines, not transport ships to take troops to Europe.
It can be argued that this debate over US force levels in Europe has been overshadowed and perhaps delayed by a more pressing NATO issue - deployment of US-made Pershing II and cruise missiles in Germany, Britain, Italy, Belgium, and the Netherlands.
The Reagan administration has had to fight very hard to maintain alliance unity over deploying these missiles as a response to Soviet SS-20 nuclear missiles in Eastern Europe. When that question is settled - either with full deployment or arms control - it can be expected that the stationing of hundreds of thousands of US troops in Europe again will surface as a major issue.