Secretary of State George P. Shultz's startling statement about the need for stronger measures against terrorists destroys the lingering myth that he is the most moderate member of President Reagan's Cabinet.

Shultz took over the baton from Alexander M. Haig, whose excesses had made him the joy of cartoonists and an embarrassment to the White House. Shultz's appointment was hailed as a return to reason and logic in the conduct of foreign affairs.

Now it has come full circle. Haig, at his extraordinary confirmation hearings, announced that combating terrorism would be the No. 1 priority of the Reagan administration. But it took his supposedly measured successor to suggest that the Constitution might have to be scrapped in the process.

From the outset, Shultz, a former professor of economics who made a name for himself as a man of reason in the Nixon years, has felt a heavy obligation to prove himself a team player. His first appearance after his appointment was at a rally for the irrational cause of a constitutional amendment to balance the budget.

Since then, he has demonstrated a willingness to step out as point man on inflammatory issues, notably on Nicaragua. He compared the nervous, hard-up Sandinistas to Nazis and when the United States was reproved by the World Court for mining the harbors of Nicaragua, he figured in the decision to refute the court's jurisdiction.

But nothing he did came near to his amazing representations on the subject of punishing terrorists. He donned a yarmulke in a New York synagogue and announced that America has to straighten up and forget the Constitution if it is to stand tall against the faceless bomb-throwers who have humiliated Reagan, the restorer of America's respect.

This country, he declared, should not become "the Hamlet of nations." It must "go beyond passive defense to consider means of active prevention. We must be willing to use military force."

In his most provocative passage, he said, "The public must understand before the fact that there is potential for loss of life of some of our fighting men and the loss of life of some innocent people."

Shades of the infamous Huston Plan of the Nixon years, when officials considered sanctioning domestic espionage and breaking into foreign embassies here to ensure national security.

Ironically, it was Vice President Bush, the president's most faithful echo and shadow, who took public exception to Shultz's Draconian solution.

Bush's initial reaction was that of anyone facing martyrdom: "I don't think we ever get to the point where you kill 100 innocent women and children just to kill one terrorist. I don't think we have reached that point." Of course, he took it back the next day.

Reagan waltzed around the edges of the Shultz blockbuster. Over the running motors that provide the sound effects for all his encounters with the news media these days, he said that Shultz had "said nothing new." Later, confirming Walter F. Mondale's campaign charges that he is the "most detached and remote president in this century," Reagan said he didn't think that Shultz was making "a statement of policy." Finally, White House spokesman Larry Speakes roundly contradicted the president. Shultz's initiative, he said, was "administration policy from top to bottom."

Ever since his warning to terrorists in his Inaugural address, Reagan has taken no action against them. His frustration reached a peak after the truck-bombing of the Marine barracks in Beirut. The French conducted a raid on suspect terorist camps, but in the end, the United States did not join in, for reasons that Shultz says should no longer apply.

The Shultz doctrine is fascinating as one of the few clues about what a second Reagan term would be like.

It is also the first time any administration official has even implicitly reproached the American people. Surely, it wasn't a patch on President Jimmy Carter's fatal "malaise" speech, but Shultz seemed to complain that creeping wimpiness on the part of a squeamish citizenry is all that stands between Reagan and swift reprisal.

As luck would have it, right after Shultz had taken out his terrible swift sword against people he can't control, some people in his direct charge stepped out of line. Twenty-two U.S. ambassadors took the unprecedented and unseemly step of endorsing the reelection bid of Sen. Jesse Helms (R-N.C.), the ultra-conservative friend of dictators and apartheid. Shultz issued a pro forma "tut-tut" statement.

Excess is contagious. If the boss says we must break the rules of international conduct to get after terrorists, surely his underlings can shatter the tradition that they represent all the people.