In the light of long personal experience, former secretary of state Henry Kissinger has concluded that the "Little State Department" in the White House ought to be abolished or, at the minimum, cut back to its original limited mission.

Its present all-encompassing operation is an unforeseen outgrowth of a National Security Council established in 1947 by President Truman to collate diplomatic and military thinking. It concluded the assignment of a White House assistant, called the national security adviser, to act more or less as a secretary for the NSC.

Who could have guessed that the national security adviser, first as portrayed by Kissinger and currently by Zbigniew Brzezinski, would come to overshadow the secretary of state and, on occasion, transcend even the president himself?

Looking back now at both his terms as secretary of state (1973-77) and, before that, as Richard Nixon's national security adviser (1969-73), Kissinger is convinced that a president (any president) should make the secretary of state "his principal adviser, and limit his security assistant to administration and coordination."

The State Department, he thinks, "should be the visible focus of our foreign policy. If the president has no confidence in his secretary of state, he should replace him. If he does not trust the State Department, the president should enforce compliance with his directives, not circumvent it with the NSC machinery."

Kissinger, as White House adviser, was witness to Nixon's humiliation of his secretary of state, William P. Rogers, who was so circumbented and kept in the dark that he was reduced to a mere figurehead. But at least everybody knew who was boss then, which is more than can be said about the present administration.

If Carter is reelected and Cyrus Vance, as he has indicated; retires as secretary of state, Brzezinski could well succeed him. In that event, he, too would probably try to combine both jobs. Meanwhile, however, nobody, including the president, knows from day to day who is in charge of foreign policy. This is the way it has seemed to shape us: secretary of state for China -- Brzezinski; secretary of state for South Korea -- Harold Brown; and, until recently, secretary of state for the Middle East -- Robert Strauss; and secretary of state for Africa -- Andy Young. The administration has also had guidance from several surrogate foreign ministers, such as Sen. Frank Church (Cuba), Sen. Henry Jackson (SALT II), Sen. sJesse Helms (Rhodesia) and Sen. Sam Nunn (NATO). That leaves Vance as secretary of what's left.

No one knew there was a national security adviser until John F. Kennedy appointed the dynamic McGeorge Bundy to the post in 1961. Under Dwight Eisenhower, the job was held by Robert Cutler, who had a passion for anonymity -- and a good thing, too, for Ike's imperious secretary of state, John Foster Dulles, would not have tolerated a rival. Nor would the strong-minded Dean Acheson, who dominated State under Truman.

But Kennedy wanted to run his own foreign policy and, brushing off State, he quickly was involved in the Bay of Pigs disaster, the grim Vienna confrontation with Nikita Khrushchev and the erection of the Berlin Wall. Lyndon Johnson followed up with the invasion of the Dominican Republic and armed intervention in Vietnam, ardently encouraged by his national security advisers.

When Nixon became president, both Secretary of State Rogers and Defense Secretary Melvin Laird wanted to get out of Vietnam as fast as possible; but, unbeknownst to them, Nixon had other ideas, the upshot being that the United States got out four years later after more heavy casualties, followed by ultimate loss of the country.

Brzenzski took over at the White House saying, "The need is not for acrobatics but for architecture." But since then he has been doing handsprings all over the globe. In fact, much of Carter's on-again, off-again foreign policy can be traced to his letting the hawkish Brzenzinski turn him on, only to let more cautious advisers turn him off later.

A coherent foreign policy, says former undersecretary of state George Ball, "requires that only one voice speak for the president." The "prevailing ambiquities," Ball observes, "confuse foreign governments," one reason being that no other country has an operation like Brzezinski's.

As Ball notes, Brzezinski "acts as a co-equal secretary over the whole spectrum of our foreign policy. He deals with foreign ambassadors, undertakes diplomatic missions, negotiates with chiefs of government, makes speeches, appears on television and gives press conferences."

Dean Acheson long ago warned that "a special adviser is most unwise to do any talking." As for Brzezinski, the sardonic former secretary of state once said, "I squeezed him dry -- there was nothing there."