Like Broadway playwrights and Oklahoma wildcatters, the presidential campaign manager is only as good as his last big hit. All it takes is one loss with the inevitable bad reviews and yesterday's genius is this morning's jerk. John Sears, Ronald Reagan's campaign manager, who was recently being alternately lionized or canonized as a genuine political prodigy, must by now be black and blue from aggravated second-guessing.

Iowa, which Mr. Reagan was supposed to win and which George Bush did win, is at the heart of Mr. Sears' fall from grace. Mr. Reagan, presumably at Mr. Sears' suggestion, skipped the Republican debate in Des Moines and was in the state barely long enough for a cup of coffee. Mr. Bush, who spent enough time in Iowa to meet the residency requirements, defeated Mr. Reagan by less than one vote per precinct, but what matters is he did beat him.

Since long before Mr. Reagan's November announcement of candidacy, the Sears-Reagan strategy has not been hidden. It was to avoid taking any position that would jeopardize Mr. Reagan's success in the general election. Gone were the oratorical excesses of earlier Reagan campaign speeches. Certainly not for the first time in recent political history, we were being presented with a less partisan Republican presidential candidate: a new, more moderate Reagan. It was a strategy that won the near-unamimous endorsement of most of the political community.

But for Ronald Reagan, after Iowa, there can be no plans for the general election. New Hampshire is almost upon him, and a second loss would be devastating. So, following the example of so many candidates before him, Mr. Reagan has gone back to what has previously always worked for him politically. Here are just a few samples of the non-general-election Ronald Reagan. In response to President Carter's reference in the State of the Union address to the possibility of cooperation with Iran because of that country's fear of the Soviet Union: "Mr. Carter is either deceitful or a fool." More of Mr. Reagan on Mr. Carter's foreign policy: "We're seeing the same kind of atmosphere we saw when Mr. Chamberlain was tapping his cane on the cobblestones of Munich." Not merely content to criticize but also wiling to suggest, Mr. Reagan has turned up the rhetorical thermostat: "One option might well be that we surround the island of Cuba and stop all traffic in and out."

John Sears' guiding maxim for winning campaigns has always been: "Make the other candidates react to you." It is a maxim that Ronald Reagan, presumably with Mr. Sears' agreement, is breaking daily. The questin is whether, in every sense of the word, he will become so "reactionary" that he moves himself right out of the ultimate running.