PRESIDENT Reagan is getting a lot of advice about how to run the world, and much of it must seem pretty confusing. Don't overthrow the Marxist government in Nicaragua, say some critics; it's not our business to install democracy there.
However, do take steps, say many of the same critics, to change the power structure in South Africa, because it is our business to install democracy there.
Armchair experts tell the President: Don't have a policy of constructive engagement with South Africa because it is an odious regime with unpalatable policies, and we mustn't be seen talking to it.
But the same experts advise: Do have a policy of constructive engagement with the Soviet Union, because it is an odious regime with unpalatable policies and we must try to moderate them.
Don't play world policemen, some constituents tell him. But the same mail brings letters urging, do topple President Marcos of the Philippines, do bring the Israelis to heel and insist they talk with the Arabs, do something about Soviet occupation of Afghanistan, and Vietnamese occupation of Kampuchea. It is all part of that healthy, and contradictory, expression of opinion that prevails in a democracy.
The President cannot reduce it to a simple formula applicable to all because the world is a complex place, and US influence varies from nation to nation.
South Africa is a good case in point. The United States abhors apartheid. It has said so and should continue to say so. But the suggestion that US influence can remake South Africa is ridiculous. South Africa has shown a conspicuous lack of response to admonitions from a string of US administrations.
Maybe there will be US sanctions against South Africa, but those are not going to topple apartheid. What should happen in South Africa is clear: Whites and blacks should sit down together to see whether they can forge a truly multiracial society in which there would be security and justice for all. The US can and should urge such a dialogue. It cannot make it happen. It cannot guarantee the outcome.
Take Nicaragua. Some of the President's extreme right-wing supporters think he should do just that, take it, expel its Marxist rulers from power, and install the democracy they promised during the revolution against President Anastasio Somoza, but which they failed to implement.
From a military point of view it could probably be done, with heavy loss of American life. Politically, it is unthinkable. Few people think Managua is run by a bunch of well-meaning Boy Scouts. But even so, Congress, public, and press would oppose unprovoked direct American military action against the regime.
US power is hobbled by geography. To take military action in Central America is one thing. To take military action in far-off Asia is another.
British Prime Minister Margaret Thatcher sent a fleet into action in cold and distant waters when she determined to recover the Falklands from the Argentines. That was a risky one-shot gamble. Few military men would recommend such a campaign under such conditions over an extended period so far from home.
The fact is that the US cannot, and should not, try to run the world. But as a superpower it has responsibilities it cannot and should not shirk.
Much of the time it will make progress by using influence and gentle persuasion on other countries. Power should be used with reluctance, but power is the necessary underpinning of diplomacy.
Communications technology, plus changing US interests, has made Americans more internationally conscious. Where once US interests were centered on Europe, dramatically expanding trade with Asia has brought Asia into the American conscience. The tragedy of starving Africa and the plight of blacks in South Africa have directed new American focus toward what was previously a very dark continent.
If all this is producing a growing sense of world family, that is good. But family members are full of individual, sometimes wayward expression. It is unrealistic to think the US can control the world family.
John Hughes is a Pulitzer Prize-winning journalist who was assistant secretary of state from 1982 to 1984.