You can take the professor out of the classroom, but you can't take the classroom out of the professor.

That thought occurred to me as I listened last week to Secretary of State George Shultz defend the Constitution and true American values in his dramatic two-day appearance at the Iran-contra hearings.

The nation's top diplomat, there to expose what he called the "guerrilla warfare" right in the corridors of the White House and to assail those self-anointed heroes who choose to lie to Congress, couldn't forget that his first love was not politics but economics.

Around the State Department, there are some Shultz-baiters -- including members of the press -- who snicker that the only thing that can snap Shultz out of Dullsville is some big economic event, such as a major devaluation or an oil embargo.

What they don't know, and what Shultz has never forgotten, is that the world's international economy is so closely linked with global strategy and security that the one can't be separated from the other. The nation is extremely lucky to have had as secretary of state in this recent period of global tensions a distinguished economist who brings to his high diplomatic office an extraordinary background that includes service as secretary of labor, secretary of the Treasury and direc-ju tor of the Office of Management and Budget.

Shultzonomics may not have left a deep impression on a committee already stunned by is more dramatic description of how he had been manipulated and left out of strategic policy decisions by adventurers who had little understanding of the Constitution. But his international economics lesson, if absorbed by Congress, could be among the most important contributions he has made.

In the middle of his testimony about treachery and infighting in the Reagan administration, Shultz -- amazingly -- took the opportunity to remind the influential senators and congressmen on the two select committees that Congress is on the verge of passing protectionist trade legislation and that they had better think twice about that.

Shultz saved his best economics advice for his concluding thoughts. After reiterating his pitch for accountable government and for effective sharing of power between Congress and the administration, the secretary delivered a strong case for global economic interdependence:

"It seems to me clear as you look to the future, as the world GNP grows, as it is disbursed around the world, we'll see more and more countries that have genuine capability, because they will have a size that will make our world different than it has ever been before. The notion of a bipolar world has long since gone, and we will have a diverse world where capability is widely dispersed."

What's so special about that? you may ask. As self-evident as it may seem that other countries -- especially since the end of World War II -- have grown in many ways, the protectionists in our midst pretend that the United States has the same relative clout and power as it did 50 years ago. Therefore, if some nation is beating us out on this or that product, it must be cheating.

The fact is, as Shultz knows, we no longer have a monopoly on being "the best" in everything: with our help, other nations have grown up. He continued his little lecture this way:

"There are smart people everywhere. And there are people all over this world that are working very hard along with their smarts. So that this spread of a capability and a capacity is going to change the structure of the world economy and the strategic situation, and we have to try to understand it.

"There is, I think, a gigantic amount of change in technology to go with this. We can see process replacing materials. . . . A clear and obvious example that everybody can see is the way in which fiberoptics are substituting for copper. . . .

"I think we can see that advances in biotechnology are changing the ability to feed ourselves, and particularly when you combine that with obvious points of how economic activity can be organized to promote production of food, Malthus is being stood on his head."

Shultz was portraying the reality that "there is no way that we can, once again, as we did after World War I, sort of remove ourselves from the world." Financial markets are global, and "production and trading of goods is worldwide." Foreign policy, as he said, depends on the extent to which America decides to stay engaged, instead of turning inward and isolationist.