Jimmy Carter would prefer to float placidly above the squalls that rage within the White House. But this gentle soul of uncertain but benign ideology has been swept up in a whirlwind that could bring peace or war.

With one ear, the president listens to the warnings of his national security adviser, Zbigniew Brzezinski, about the evil designs of the Russians. With the other, Carter harkens to the pleadings of Secretary of State Cyrus Vance for detente.

Brzezinski has tried to tell the president that the Soviets are testing his mettle, that they view any appeasement as weakness, that they are playing hardball against his softball. The Soviet drive into Afghanistan will continue all the way to the Persian Gulf oil fields, Brzezinski warns, unless the United States pushes back.

But in Vance's opinion, the Soviets moved into Afghanistan to buttress their own borders against the spreading Moslem inflammation. Brzezinski's countermoves, Vance feels, will merely cause the Soviets to tighten their grasp on Afghanistan. He is convinced that the Soviets would like a graceful way out. But Brzezinski, by his provocative behavior, is foreclosing that possibility.

The president's head can be turned by the articulate Brzezinski, but his heart belongs to Vance. This has sometimes produced a schizophrenia in foreign policy, with Carter talking like Brzezinski but acting like Vance.

At the outset of his administration, for example, Carter warned the Soviet Union against meddling in Ethiopia. Yet he failed to carry through on any of the threats that had been communicated to Moscow, and the Soviet bear added another cub to its family.

When the shah's rule was threatened in Iran, the president instructed a naval task force to sail from the Far East to the Persian Gulf. But when push came to shove, Carter canceled the order and the task force dropped anchor at Singapore.

Carter's wishy-washiness was exposed again when U.S. intelligence agencies discovered a sizable force of Soviet combat troops in Cuba. At first, the president waved his wooden sword; he declared the Russian move was a "very serious matter" and was "not acceptable."

Three weeks later, he sheepishly accepted the presence of the Soviet troops on grounds that he had "received assurances" from the Kremlin that the brigade would pose no threat to the United States. The Russians have continued to expand their military operations in Cuba, causing grave alarm in the Pentagon.

The Afghanistan crisis has now precipitated a series of impulsive responses from the man in the White House. He has talked of supplying arms to Pakistan to fend off any Russian move in that direction.

But he apparently has forgotten the experience of last year when the United States rushed $400 million worth of weapons to North Yemen to counter threats from communist-dominated South Yemen. Pentagon sources now admit that the emergency decision resulted in a classic foul-up.

Many of the arms were never delivered; some are lying idle in Saudi Arabia or North Yemen. Sources have told us horror stories of Yemeni soldiers driving their tanks into ditches and abandoning them. Training programs for the Yemeni forces have bogged down. North Yemen has turned to Russia for arms and has indicated an interest in reunification with South Yemen -- an event that could put both countries into the Soviet orbit.

After the Russians invaded Afghanistan, Brzezinski flew to Pakistan and visited the Afghanistan border in a one-man show of strength. But some of my sources believe that the White House adviser's mission was a "fiasco" and a "totally botched job" that could backfire badly. Brzezinski is less interested in helping Pakistan or achieving the liberation of Afghanistan, said one source, than he is in trying to "score some points against the Soviets."

The president's erratic diplomacy has clearly upset our European allies. West German Chancellor Helmut Schmidt has privately questioned Carter's tactics, and the always testy French refused to rubber-stamp a package of economic retaliation that the president urged on the European community.

A meeting of Western foreign ministers, which was scheduled to take place in Bonn last week, was scuttled when the French suddenly announced they would not attend. This forced a move by the Carter White House to patch up differences. Quiet consultations in Washington and Paris and some smooth diplomacy by Vance during last week's European trip, it is hoped, will repair some of the damage wreaked by Jimmy Carter's precipitate diplomacy.