A great nation is sometimes like a mighty ocean liner with a small rudder. It tends to change course slowly, ponderously. And if the captain hauls too hard or too long on the wheel, it may swing past the ideal direction and end up tacking between extremes.
The United States today is clearly swinging back toward a more forceful - sometimes military - stance in world affairs. To say this is not to make a judgment on whether that is right or wrong. Historians will argue over Washington's recent foreign policy zigs and zags for years to come.
What is plain, however, is that this country's post-Vietnam comparative passivity is being replaced by renewed activism. The bow of the ship of state is shifting to starboard. The trend has global implications.
The turning point was Lebanon; not this week, with the buildup of US naval forces in the eastern Mediterranean; nor last month, with the shattering explosion which took the lives of more than 200 marines. Rather, the real turning point occurred last year when the Reagan administration decided upon the first major new deployment of American ground forces overseas since the end of the Vietnam war.
In August 1982, a little less than a decade after US troops completed their 1973 withdrawal from Vietnam under the Paris accords, President Reagan dispatched the Marines to Lebanon to help supervise the evacuation of the Israeli-battered remnants of PLO forces.
True, US marines had been sent into Lebanon before. Back in July l958 President Eisenhower had landed a 10,000-strong force on Lebanese beaches to shore up a shakey regime requesting assistance as it struggled to quell armed uprisings among its own people. What's more, President Reagan's much smaller contingent (less than 1,000) went into Lebanon last year as part of a hastily-assembled international peace force. France and Italy also joined the exercise.
Within three weeks, that initial American force had pulled out. But the precedent had been set. And within another three weeks, in the wake of the massacre of Palestinian civilians in two Beirut refugee camps, the Marines were back with French, Italian, and British cohorts for a much longer and more difficult stay.
President Eisenhower's forces left in about three months. President Reagan's forces are still there 13 months later, with the way to bring them out far from clearly defined. The Israeli invasion last year created a power vacuum at the center of the Lebanese body politic - one that the Marines and American diplomacy are desperately endeavoring to fill.
Meanwhile, the Navy's hard-pressed carriers shuttle back and forth between the eastern Mediterranean Sea, the Persian Gulf (where Iraq and Iran, like weary Sumo wrestlers grappling in mud, prolong their bitter, three-year conflict), the Caribbean island of Grenada, and the coasts of Central America - with the battleship New Jersey adding its potentially fearsome firepower from time to time.
At its height, the Vietnam war drew into its maelstrom some half a million American troops. The period of popular revulsion which followed dictated upon United States leaders, whether they liked it or not, a radically different, hands-off foreign policy. For a while this was termed ''the Nixon doctrine,'' with a theme of bolstering the locals rather than allowing the US itself to become directly involved. Back at home, many Americans went through a period of introspection and self-doubt.
The fall of the super-bolstered Shah of Iran partially eroded the Nixon doctrine. And even while President Carter was still at the US helm, the American mood had begun to change.
After the Soviets invaded Afghanistan just before Christmas l979, Jimmy Carter declared that his opinion of the Russians had ''changed most drastically in the last week,'' imposed a grain embargo and an Olympic boycott on Moscow, and began to tighten up American security. Since then, President Reagan has swung the ship's wheel over still further - with the Marine deployment in Lebanon being a crucial turning point.
The questions now are:
Does the present more activist course reflect, in fact, the central flow of American national interests across the globe? Is it a healthy revival from an overly passive post-Vietnam past? Or is it itself the beginnings of a new excessive swing?
It takes foresight, skill - and time - to keep the ship on a steady course.