"I could do the easy political thing," Richard Nixon was fond of saying, just before doing it. The easy political thing now is to catch President Reagan in the contradictions between what he said about Jimmy Carter's hostage crisis and what he's doing about his own.

You can almost hear the Carter people smugly saying, "Welcome to the club." The jibe is justified: presidential candidate Reagan was scathing in his indictments of the Carter administration's handling of the hostage crisis in Iran. In his first White House days, he offered a pointed, posturing alternative: "Let terrorists be aware that when the rules of international behavior are violated, our policy will be one of swift and effective retribution."

But that was a pronouncement. A policy is a course of action as it is actually pursued. Last week, in his subdued and sensible handling of the crisis of TWA 847, the president was talking counter-terrorist policy. What he said makes it unmistakably clear that he understands the club's first rule: With a case at hand, none of the natural reflexes -- the abstract solutions, the absolutes of always retaliating and never negotiating, and certainly never rewarding terrorism -- are quite so appealing from the inside looking out as they appear to be to the blowhards on the outside looking in.

The president came on strong: "I am directing that the following steps be taken." But the steps were the tipoff: The secretaries of transportation and state would "explore" an expanded sky-marshall program and U.S. citizens would be advised not to travel through the Athens airport. What he said about retaliation and carefully avoided saying about the diplomatic route made restrained frustration his dominant theme. More important, the sum of what the president said left the way wide open for a strategy of semantics, artful ambiguity and the connection of seemingly unrelated acts by the fine, invisible wires of diplomacy.

The result is that no damage was done to the one prospect for a solution. For all his ritual insistence that "America will never make concessions to terrorists," the president made plain by his evasions that one way or another the release of the hostages will hinge on the ultimate return by Israel of young Shiite prisoners scooped up by the Israeli army as it withdrew from southern Lebanon. Israel had already returned over 400 of the original 1,100; it was ready to start releasing the rest when the hijacking occurred. Only when Nabih Berri, the Shiite leader, tied the hostages and the Israeli Shiite prisoners as a quid pro quo was the issue of "rewarding terrorism" introduced.

There followed an "after you, Alphonse" exchange with Israel demanding that the United States take the rap for insisting on the release of the Shiites and the United States insisting it would never put such pressure on a friend. With the International Red Cross as the fall guy, it should not be beyond the wit of Israel and the United States to find a way around this obstacle.

That is not at all to predict how this crisis will play out, given the lack of cohesion of Lebanon's nongovernment. But in the course of pointing out how this made his problem different from Carter's, Reagan made a dubious argument that Iran, at least, had a government, in an interesting way.

What he had in mind, he said, when he made his statement on terrorism in January 1981, was that "you have a great many more opportunities then to find vulnerabilities in another government, and things that you can say in return, and that you can offer as a trade."

Offer as a trade? That does not sound like a man unalterably unwilling to deal. Still less did the president sound inclined toward "swift and effective retribution." Retaliation, he said, seems to some people to mean "striking a blow in a general direction" but "the result would be a terrorist act in itself and the killing and victimizing of innocent people."

I would not suggest that this adds up to a comprehensive policy. But it suggests a consistent thread. When asked four months after the Marine catastrophe at Beiruit airport why he did not retaliate, Reagan told The Wall Street Journal that this could result in "killing somebody . . . in revenge" without knowing "whether they had anything to do with the dastardly deed or not." The Ronald Reagan of that interview more than a year ago was the Ronald Reagan of last week. He was "as frustrated as anyone," knowing "you can't just start shooting without having someone in your gun sights."