It is kind of mutual protection bond that exists between long-time members of an exclusive club, and, over the course of four days in Rome, Secretary of State Alexander M. Haig Jr. exploited it in hopes of getting a new grip on the foreign policy reins that had seemed to be slipping from his grasp.

This week's North Atlantic Treaty Organization meeting in Rome demonstrated that a positive chemistry between Haig and the foreign ministers of America's West European allies still exists. It demonstrated, too, that they are disturbed by speculation about Haig's being in trouble with the senior White House staff; by their actions, they sent President Reagan a clear signal that they want Haig kept on the job.

That Reagan got the message was underscored by the scene at the White House on Wednesday when the president, with Haig at his side, appeared before the press to exclaim gushingly, "He returns home in triumph," and to laud the secretary for his performance "in a situation that could have been critical for us in regard to our allies."

In actuality, what happened in Rome did not have the cosmic significance implied by the president's full-flourish rhetoric. Some fairly important horse-trading did take place: the United States tried to ease some European concerns by promising to seek negotiations with the Soviet Union on limiting European-based nuclear missiles, and the West Europeans expressed their appreciation by tacitly backing the Reagan administration's policy of linking detente to how well the Soviets behave on the international scene.

However, despite Reagan's assertion that these actions averted "a situation that could have been critical," the outcome of the NATO meeting could have been predicted in advance. The United States, if it wants to ward off rising European sentiment against stationing U.S. missiles on the continent, had no choice other than to promise an effort at arms-limitation talks. And the Europeans, given their concern about the effects of a possible Soviet intervention in Poland, couldn't avoid joining in a tough warning to the Soviets about the consequences of aggressive behavior.

Instead, what made the Rome meeting significant was the way in which it pointed up Haig's role as the official in the Reagan administration who is best able to act as an interlocutor between West European leaders and what they still regard as an untried and unpredictable new force in Washington.

Through his service as deputy to Henry A. Kissinger in the Nixon administration and his five years as NATO's military commander, Haig has come to know Western Europe's principal leaders on intimate, first-name terms. He is trusted by them as someone who understands their problems and concerns and who can be counted on to see that their views are taken into account in the formulation of U.S. policy.

No one else in the administration can fill that bill. Defense Secretary Caspar W. Weinberger is regarded by the Europeans as an unsophisticated novice, and key White House aides like Edwin Meese III and James A. Baker III are totally unknown quantities in the capitals of Europe.

For those reasons, the Europeans are known to feel that they have almost a vested interest in Haig remaining in office; and the NATO meeting -- an arena that is requivalent to Haig's home turf -- proved an ideal vehicle for them to band together and give him a boost with the boss back home.

Haig clearly recognized the advantages and exploited them fully. In the internal administration policy discussions preceding the meeting, he is known to have championed the argument that European leaders like West German Chancellor Helmut Schmidt had an important stake, for domestic political reasons, in a U.S. reaffirmation of past commitments to pursue missile-limitation talks.

His success in getting Reagan's go-ahead on renewing the commitment delighted the Europeans. At the same time, his performance in Rome -- both in the formal NATO sessions and in private talks with all 14 of the other ministers -- gave him the chance to demonstrate to those watching from the White House that he had submerged his normally temperamental, lone-wolf style to the team-player approach favored by the president.

In fact, the joke that emerged from Haig's Rome performance was that he had learned two new words -- "President Reagan." Again and again, he is known to have stressed to everyone with whom he talked that he was there to explain and to represent "President Reagan's policy," that it is Reagan who wants better relations and consultations with the allies and that Reagan is determined to instill a pattern of consistency and leadership in the alliance.

The Europeans, for their past, went out of their way to make clear their feeling that Reagan couldn't have sent a better messenger than Haig. When the final communique was issued on Tuesday, it read almost like a speech Haig had made to the American Society of Newspaper Editors 10 days earlier: warning the Soviets sternly against intervention in Poland, echoing Haig's special concern about communist troublemaking and support for insurgent groups in the Third World, and citing Soviet conformity to a code of good behavior as the basis for future detente initiatives.

Whether the rhetoric of the communique will be translated into actual practice as the NATO allies confront specific situations in the months ahead is still an open question. But Haig left Rome with NATO, nominally at least, lined up on paper behind an agenda that sounded like a detailed list of the policies he has been preaching.