Perhaps the worse mistake Jimmy Carter made as president was his failure to decide how foreign policy should be run and who should run it. It was extremely costly for both him and the country.

Nevertheless, it now appears that Carter's successor is about to fall into the same error. The abrupt appoint of Vice President George Bush as a "crisis manager" of foreign policy cannot be counted on to end the administration's growing disarray on this vital front.

It is, at best a makeshift solution, since no vice president can effectively serve as a part-time secretary of state. The White House explanation is that "President Reagan's choice of the vice president was guided in large measure by the fact that management of crises has traditionally -- and appropriately -- been done within the White House."

It would be closer to the mark to say that some presidents have dominated their own foreign policy, just as other chief executives have been content to let the secretary of state run the show.

Experience suggests that either system can work if it is consistently followed, but Carter proved that vacillating between the Little State Department in the White House (better known as the National Security Council) and the formal State Department at Foggy Bottom is a sure path to confusion and failure.

Under President Truman, two dominant secretaries of state, Dean Acheson and Gen. George Marshall, exerted unquestioned authority over their domain. The same situation prevailed even more markedly under President Eisenhower, who made John Foster Dulles the exclusive custodian of foreign policy. Even Kie himself deferred to Dulles.

The rise of the Little State Department began with President Kennedy, who had a deep personal interest in international affairs and wanted to direct his own policy. He and his national secruity adviser, MdGeorge Bundy, simply took over, with little regard to the State Department.

Kennedy was succeeded by another assertive president, Lyndon Johnson, who also intended to run the show himself, and did. It was Richard Nixon, and Henry Kissinger, however, who turned the State Department into a cipher -- that is, until the commanding Kissinger himself because the secretary of state, at which point the department overnight regained ascendancy.

Whatever the shortcomings of the contrasting systems, they both had the virtue of being consistent and coherent. Neither the American public nor the rest of the world was in much doubt about U.S. policy or who was in charge.

Jimmy Carter could never decide how to delegate responsibility for foreign policy. He continuously fluctuated between the cautions, but sound, advice of Cyrus Vance, his secretary of state, and the more flamboyant recommendations of a White House staff that, on the whole, was primarily interested in the political fortunes of the president. It all culminated in the ill-fated Iran hostage resuce raid, and the resignation of Vance. It was a disaster for Carter.

As secretary of state, Gen. Haig may seem too strident to many Americans, but so far his hard line has been in the Reagan tradition, and his anti-Soviet rhetoric has certainly not been tougher than the president's. Moreover, Haig's controversial El Salvador policy is very much in the Reagan image.

Logically, it is not altogether clear why Reagan feels it is necessary to rein in Haig and reduce his authority and prestige. It is true that the administration has been embarrassed by a recent rash of alarmist statements on foreign-military policy, some of which have been repudiated by the White House, but very few of these blurts were made by the secretary of state.

Although Edwin Meese, the White House counselor, originally said the administration would "speak with one voice," it was Meese, not Haig, who first announced that the government might resort to military action against Cuba.

It was Richard Allen, the president's national security adviser, who outraged our NATO allies by accusing them of harboring "outright pacifist sentiments."

It was Richard Pipes, the Soviet expert on Allen's staff, who was disavowed by the White House after saying war with the Soviet Union was inevitable if the Russians did not abandon communism.

It was John Lehman, secretary of the Navy, who had to be disavowed when he suddenly called for breaking the U.S.-Soviet agreement on the limitation of strategic arms.

It was Caspar Weinberger, the secretary of defense, who startled both NATO and the White House by reviving the possibility of deploying neutron missiles in Western Europe.

And it was Reagan's new ambassador to the United Nations who embarrassed the administration by meeting with South African military officers in New York, although they had been ruled persona not grata in Washington.

All in all, it is difficult to see why out allies are less uneasy with Haig than with the rest of the administration. So, unless the president is ready to run foreign policy himself, the authority of Haig should be sustained, not undermined.