AN IDEA central to the United States' global strategy of the past 20 years has been to have China move from Russia's side to America's and stay there. Western Europe and Japan, two other great power centers, have spun in a common orbit with this country since World War II. China had to leap high barriers of ideology and history to make common strategic cause with the United States, but it has been doing so, making Moscow tend its Asian ''flank,'' for nearly a generation. There is not so much talk now as there used to be about the Washington-Moscow-Beijing ''triangle,'' but China's power and potential make its orientation crucial to the global stability that is the continuing American goal.

This is the broad stage on which to view the latest small gestures by the Soviet Union and China. Mikhail Gorbachev, to cultivate Beijing, has brought about some improvements in direct dealings between the two Communist states and has taken steps to meet ''encircled'' China's three stubbornly maintained conditions for ''normalization'' -- easing Soviet military pressure on the Chinese border, leaving Afghanistan and seeing to its ally Vietnam's withdrawal from Cambodia. Just the other day Moscow advanced a new Afghan formula, and Beijing gave Mr. Gorbachev a rare forum, a press interview, to make his case for better relations -- and for a Sino-Soviet summit. The Chinese reiterated their familiar summit condition that Moscow get Vietnam out of Cambodia, but no doubt Mr. Gorbachev will keep pressing.

Some anxious observers, noting the differing interests and perspectives that still mark Sino-American relations (China's missile shipments to Iran, for instance), wonder whether the friendship between Beijing and Washington can be sustained. They ask whether the agile Mr. Gorbachev may not be preparing to swoop in and draw China back to or toward the Soviet side.

For Moscow to normalize relations with China, with or without weakening China's friendship with Washington, could be a substantial strategic coup. The evidence is thin, however, that anything so far-reaching is in the offing. Further progress -- meaning Soviet concessions -- on the three key foreign issues is conceivable, but the United States will remain better placed to aid China's modernization and security alike. Americans ought to be as ready and able as Soviets and Chinese to work all legs of the Washington-Moscow-Beijing triangle at the same time.