THE KEY PLAYERS : THE CRISIS IN THE WHITE HOUSE : John M. Poindexter : <i> ‘Principle of Speaking Soft and Carrying a Big Stick’ </i>

After John Marlan Poindexter moved quietly into the West Wing office reserved for the President’s national security adviser, a key White House official remarked, “He embodies the principle of speaking softly and carrying a big stick.”

A balding, bespectacled, round-faced Navy man, Poindexter did not fit the mold cast by such flamboyant predecessors as Henry A. Kissinger, Alexander M. Haig Jr. and Zbigniew Brzezinski. Although he retained the rank of vice admiral, he forsook the uniform for dark, understated business suits.

In spite of his relatively low-profile personality, however, Poindexter was in the thick of the foreign policy operation during his 5 1/2-year White House career, which he began as an arbitrator of bureaucratic conflicts and ended as a central figure in the Iran arms-and-hostages deal.

Poindexter was the fourth person to hold the title of national security adviser in six years in the Reagan White House.

He joined the White House staff in June, 1981, with the mid-level rank of military assistant to the national security adviser. From this post, he rose to deputy assistant to the President for national security affairs in October, 1983, and then to national security adviser last December.

But after just 11 months among the most senior Administration officials, Poindexter may yet find a home in the Navy. On Tuesday, the 50-year-old Poindexter resigned after it was disclosed that his staff had overseen the secret transfer of money, paid by Iran for arms, to accounts funding the contras fighting Nicaragua’s Marxist-led government.

It was by no means the first time that he had found himself in the midst of controversy, despite his efforts to shun the public spotlight.

In October, 1983, it was Poindexter who instructed White House spokesman Larry Speakes to respond by saying “preposterous” in answering a reporter who asked whether U.S. forces were about to land on the Caribbean island of Grenada.

It was Poindexter who was the architect of plans to intercept the Egyptian airliner carrying the hijackers of the Achille Lauro cruise ship in October, 1985: He remembered a World War II interception and called a vice admiral at the Pentagon to determine if a similar exploit could be carried out.

And it was Poindexter, holder of a Ph.D. in nuclear physics from Caltech, who was said by a Pentagon official to have been deeply involved in the initial White House efforts that have led to the Strategic Defense Initiative, the program designed to determine the feasibility of building a “Star Wars” space-based defense against nuclear missiles.

And in private life, it was Poindexter who built a computer for his car to keep precise track of his gasoline mileage and travel times.

Poindexter, who graduated first in the class of 1958 at the U.S. Naval Academy, not surprisingly sped through the ranks, holding several commands at sea. In the 1970s, he served as an assistant to Navy Secretary John L. Warner and Adm. James L. Holloway III, the chief of naval operations.

And, while his future remains uncertain, it was Poindexter who helped persuade President Reagan to name Adm. Carlisle Trost as the chief of naval operations earlier this year, and it is to Trost’s Navy that Poindexter may return.