When Secretary of State George P. Shultz decided to make a speech last week setting out his strongly held convictions about how to deal with terrorism, he got an assist in articulating his thoughts from a little-known State Department office called the "policy planning staff."

Shultz's latest argument that the United States should strike back at terrorists and be prepared to use force in Third World conflicts created a major stir. It was widely viewed as an attempt to influence the administration's debate about terrorism toward his position and away from the more cautious views of Defense Secretary Caspar W. Weinberger.

To ensure that his ideas would register with maximum impact, Shultz spent innumerable hours with key members of the policy planning staff in back-and-forth discussion, rewriting and editing before coming up with the 20-page text that he delivered before a symposium at Fort Leslie J. McNair.

It was a striking example of the unseen but highly influential role that the approximately 25 members of the planning staff play as the in-house "think tank" that helps the secretary to chart policy initiatives and to articulate them in the administration and before the public.

Because it maintains such a low profile, the policy planning staff's functions aren't even fully understood in the State Department, where many Foreign Service officers tend to think of it as essentially a speech-writing apparatus. That's because the most visible part of its operations are reflected in its contributions to the speeches and congressional testimony made by Shultz and other senior department officials.

However, that view is disputed by Peter W. Rodman, who has served as policy planning staff director for the past year. Rodman, a one-time aide to former secretary of state Henry A. Kissinger, is himself an accomplished wordsmith whose touch is evident in almost all of Shultz's speeches. But he notes that helping the secretary fine tune his rhetoric is only one of his functions, and he adds that only two of the staff members working under him are engaged full-time in writing speeches.

Other officials familiar with the policy planning staff's work said that its principal influence rests in the fact that it has direct access to Shultz. That enables the staff -- a mix of Foreign Service officers, bureaucrats on loan from other agencies and temporary recruits from universities -- to supply him with a constant flow of position papers and memos raising questions about policies, suggesting alternative courses of action and acting as an early-warning system for what its staff experts see as potential future problems.

While some of these papers deal with long-range matters, department sources said that Shultz increasingly has relied on the policy planning staff to provide him with advice on the entire spectrum of immediate policy questions.

Because it is independent of the bureaus responsible for day-to-day policy toward specific regions such as Europe or functions such as arms control, it is able to play what one official called "a devil's advocate role, sometimes agreeing with the conventional wisdom and sometimes going against the grain."

In addition to helping Shultz to stake out and enunciate the department's approach to terrorism, its influence also has been evident in such recent policy initiatives as the administration's new strategy for dealing with the international debt problem, the probing for better relations with the Soviet Union and the attempt to revive the Middle East peace process.

Such participation represents a reversal of Shultz's initial ideas about the proper role of the policy planning staff. It was founded in the postwar period by George F. Kennan, the architect of the Truman administration's "containment" policy toward the Soviet Union, and was supposed to concentrate on what one official called "big-picture, looking-into-the-future concepts."

Two years ago, in an attempt to return to that concept, Shultz formed a five-member council, composed of senior career diplomats and academicians recruited from outside, to head the policy planning staff. Their task, he said at the time, would be "to stand back and think more broadly and strategically about problems other than what is immediately in front of you."

However, department officials, while acknowledging that the council represented a high degree of talent and expertise, said that the concept didn't work well because it imposed an unwieldly extra layer of bureaucracy between Shultz and the staff. More importantly, as one official noted, the concept "didn't square with the reality of the extraordinary demands on his time. You had a lot of high-powered talent that didn't really have the access on which the concept was premised."

As a result, the council gradually broke up, its career members moving to ambassadorships and the outsiders returning to academia. Rodman, the sole remaining member of the original group, recommended to Shultz that the council idea be scrapped, and last May, the secretary issued a directive putting the policy planning staff back under a single director.