YOU HAVE TO LOOK in the cracks for any hope we won't take military action in Central America. Anything sensible being done to avert it is being done on the sly.

This week, State and Defense presented a united front for stern, although unspecified, armed intervention against Castro, whom the administration regards as "the source" of the bloody civil war in El Salvador.

On Monday, Thomas O. Enders, assistant secretary of state, went before the Senate Foreign Relations Committee and told them of a "tightening embargo." Havana, he said, is creating economic and political danger in the region.

Fast on his heels, from Defense, came Fred C. Ikle, under secretary for policy. He described Cuba as a "crown colony of Communist imperialism," the scene of a massive military buildup, and a threat, really, to the entire Western world -- since NATO supplies in the event of war, "would transit by sea from gulf ports through the Florida Straits and onward to Europe."

Enders, of course was a stand-in for Alexander Haig, the secretary of state, who talks about Cuba as if it were Germany in 1939. Ikle was the understudy of Casper Weinberger, the secretary of defense, who, mysteriously, never talks about Cuba at all.

Why this is so is one of the real conundrums of Washington.

It is almost as if the pair had had some kind of a Potsdam Conference, at which they divided up the world. Weinberger, who like most Californians, regards Europe as a distant place, with little sunshine and many old cities, and a strange aversion to neutron bombs and nuclear missiles, got Europe.

On the other hand, Haig, who as NATO supreme commander, developed rapport with European leaders, drew Central America, which is infested by guerillas, a class of people which makes him see red.

The outcome of this curious division of labor is that Weinberger exhorts a jittery Europe to rearm. And Haig, who frightens even our Central American allies, weekly escalates the rhetoric in the Caribbean and presses in public for "military options" -- which the post-Vietnam Pentagon supposedly opposes.

Usually, the White House resolves policy questions of this magnitude, but this is not the case with Reagan. When Edwin Meese, Reagan's big enchilada on both foreign and domestic policy, was asked if he cleared Haig's statements, he was quite taken aback at the idea of "censoring Al Haig."

The truth of the matter is that Ronald Reagan, whose only counter to the unease was a declaration that we had "no plans for putting Americans in combat any place in the world," does not care greatly about foreign policy. But hawks are quick to point out that such a ban would not rule out a blockade of Cuba, which is favored by those who are aching for the United States to give the Russians a punch in the nose, just about anywhere in the world.

Haig has succeeded in frightening our friends in the neighborhood, Venezuela and Mexico, who squawk at the thought of military intervention. He has also had some success in Nicaragua, where a jumpy and harsh Sandanista government is frantically increasing its military forces to counter Haig's unspecified and unremitting warnings of dreadful things to come.

He has also rattled Sen. Chris Dodd (D- Conn.), who suspects the administration might try something martial while Congress is off on recess.

He noted to Ikle that the bullying approach was more worthy of the Soviets than us.

Sen. Claiborne Pell (D-R.I.), having heard Ikle's description of Cuba's malign might, observed mildly that he finds Cuba "more of a nuisance than a menace."

As for El Salvador, the people of Rhode Island, with close ties to the Maryknoll order, "are more concerned about the murder of four nuns in El Salvador and the ongoing violence there than about any foreign policy matter in the last few years."

Ikle asked indignantly if Pell's constituents were concerned about the "suppression of freedom in Nicaragua , the exporting of arms and the buildup of the armed forces."

But there is some evidence that for all his bellicose ranting, Haig really does not want to go to war in Central America. It goes with the way to hold his own in the hawkish White House councils, to cover his dovishness about Europe.

In September, for instance, he sent Enders to Nicaragua to talk to the Sandanistas. Nothing came of it, but for people who prefer conversations to blockades, it was a sliver of hope. In November, in Mexico, he himself had a secret meeting with the vice president of Cuba. This has never been confirmed or denied by the authorities. Ikle, and his two confederates from the Pentagon were happy to say they knew nothing about it.

And just this week, two El Salvador guerillas actually were received at Foggy Bottom. State doesn't want to talk about it. It may not mean a thing. But it is something. You have to do sensible things by stealth in this administration, and let's take them any way we can get them.