AS FORMER allied commander in Europe of the North Atlantic Treaty Organization, Alexander Haig is the latest of a long line of generals-diplomats to approach the elderly Chinese revoluntionaries headquartered just beyond the walls of Peking's Forbidden City.

Haig made the trip before, as deputy to national security adviser Henry A. Kissinger, when Haig headed the advance party for President Nixon's "breakthrough" to China in 1972, after Kissinger laid the groundwork in such secrecy that the federal bureaucracy -- including Secretary of State William P. Rogers -- had no prior knowledge of Kissinger's first trip.

Memories of an electric mix of American emissionaries in the last 40 years are etched into the minds of the men meeting with Haig.

Among them were born-in-China or lifelong specialists on the Middle Kingdom: career diplomats in World War II and the immediate postwar years such as John Paton Davies Jr., John Carter Vincent, John Stewart Service. They sought, a generation earlier than Nixon and Kissinger, to draw China toward Tito-style independent communism, before Tito's Yugoslavia dared to defy Soviet domination. In the McCarthy era, when many Americans were led to believe that traitors in the U.S. government "lost China" to Communist control in 1949 -- as though a nation with nearly a quarter of the earth's population could be disposed of by the United States like a lost umbrella -- these men and many colleagues paid with their Foreign Service careers for premature wisdom.

There were compatriots, cut from military cloth, who also were Old China Hands, especially choleric Gen. Joseph W. ("vinegar Joe") Stilwell. He feuded furiously with Nationalist Chinese Generalissimo Chiang Kai-shek over whether the American priority in Asia during World War II should have been defeating the Japanese -- to which Stilwell was committed -- or positioning Chiang to crush the Chinese Communists.

There were also non-China-specialists, notably Gen. Patrick J. Hurley (former secretary of war under President Hoover). As wartime ambassador to Nationalist China, Hurley clashed with Stilwell and his Foreign Service advisers by championing Chiang's cause; he blocked attempts to Mao Tse-tung and Chou En-lai to meet with President Roosevelt in Washington in 1945, and ultimately Hurley became a prime accuser of the Old China Hands.

At the summit of military, and then diplomatic, eminence, there was Hurley's predecessor, Gen. (later secretary of state and secretary of defense) George C. Marshall. His name later graced the Marshall Plan for reconstructioning Western Europe, but he could fulfill the hopeless mission of mediating China's civil war.

Haig as secretary of state now tries his luck in a nation which traces its civilization to the Neolithic period (five to six thousand years ago), and its primitive ancestors to "Peking Man" (some 400,000 years earlier).

China's leaders always take a long view of history. In 1960, Haig was a major in the Army and a graduate student in international relations at Georgetown University, and Ronald Reagan was president of the Hollywood Screen Actors Guild, when Deng Xiaoping was in Moscow as secretary general of the Chinese Communist Party, challenging Soviet Premier Nikita Khrushchev.

The Soviet-Chinese clash was exploding behind the scenes, although the United States officially failed to see even cracks in the Communist "monolith." Behind public pledges of undying Sino-Soviet Friendship, Krushchev in private was vilifying the Chinese leadership as "madmen . . . wanting to unleash [nuclear] war." In the summer of 1960, the Soviet Union summarily pulled out of China its key technicians on whom China was critically dependent. They carried off even the blueprints for plants under construction -- as well as China's expectations for receiving a Soviet "sample" atomic bomb.

Henry Kissinger, despite his fascination with China and its rulers, cautioned in his memoirs:

"For all their charm and ideological ferver, the Chinese leaders were the most unsentimental practitioners of balance-of-power politics I have encountered. . . . [In 1971-72] Peking and Washington were entering a marriage of convenience transformed into an emotional tie primarily by Chinese psychological skill and American sentimental recollection of a China that no longer existed, if ever it had. Once China becomes strong enough to stand alone, it might discard us. A little later it might even turn against us, if its perception of its interests requires it. . ."