American arms sales to the Communist Chinese? Not now, and maybe never. But it is some measure of how far the process of "normalization" has carried us that in mid-May a team of Communist Chinese defense experts began a tour of American military bases and industrial plants -- IBM Westinghouse, General Motors, American Motors, Honeywell -- with a side trip to Disneyland.

Its mission: to prepare for the arrival on May 25 of Vice Premier Geng Biao, Peking's closest counterpart to U.S. Secretary of Defense Harold Brown.

Last January, Brown made the first visit to the Peoples Republic by any American defense official. Similarly, Geng and his entourage mark the first trip by Communist Chinese defense officials to the United States. That has a symbolic importance by itself.

But much more than symbolism and protocol are involved here. There will also be serious talks between Geng and President Carter, Vice President Mondale, Secretary of State Muskie and, of course, the top people at the Pentagon. Real weapons aside, Geng is understood to have a considerable shopping list. Nothing flashy (like an F15 or lethal by design, but support equipment of a particular value to a Chinese military establishment that is long on manpower but exceedingly short on modern technology.

No great flood of orders is expected; only relatively few decisions may be reached. But to appreciate the real siginificance of the visit of Geng Biao, you have to see the way it adds, however modestly, to the seemingly slow, excruciatingly subtle and highly complex shifts that have been taking place in the U.S.-China military relationship since the big Nixon breakthrough to "normalization" in 1972.

To do that you need to be at least aware of the close but crucial distinctions that the United States and its allies make between arms (tanks and missiles), military support equipment (radar, trucks) and "dual-use technology" (computers) of commercial as well as military value.

Prior to 1972, China was off-limits for anything with military potential, not only as a matter of American policy but as a matter of policy with out allies (NATO, Japan, Australia, New Zealand) as well, under the collective screening system known as COCOM. This was tougher than the treatment of the Soviet Union, for which some "dual-use technology" was permitted.

From 1972 to 1978, with almost no exception, there was a shift to "evenhandedness"; the Chinese and the Russians were on an equal footing. That amounted to American leaning toward Peking at Moscow's expense, in power-balancing terms.

Then, in 1978, President Carter accentuated the tilt by beginning, on a case-by-case basis, to permit the sale of some "dual-use technology" to China that was denied to the Soviet Union. One notable example: the offer of a high-technology communications ground station, giving the Chinese a link to a satellite called Landsat D, which is designed to survey land masses and feed back data on crop conditions.

That was the beginning of the so-called "China differential," which established a clear discrimination in favor of Peking. Then came the Soviet invasion of Afghanistan. On Jan. 4, the same day that the administration announced a number of sanctions directly against the Soviet Union, Carter also made two highly technical decisions carefully calculated to widen the "China differential" in important ways; the Afghan connection was unmistakable.

One was to put China in a distinctly different category from the Soviet Union, so that certain "dual-use technology" could be made available to Peking as a rule, rather than as a case-by-case exception. One effect will be to cut at least some of the nearly endless red tape in American licensing procedures and COCOM review.

The second decision was to open up strictly limited opportunities for the Chinese to buy certain items of military equipment -- trucks, over-the-horizon radar, communications gear, helicopters and other items specifically designed for military use.

The purpose of the Geng visit, as one Pentagon official explains it, is "to give substance to the Jan. 4 decision."

Nothing very splashy about that, it is conceded all around. But in these matters, the direction and the momentum often count for more than the pace. The Chinese aren't asking for arms. For one thing, they don't have the foreign exchange to pay for them. What they appear to want is technology so that they can build their own weaponry, free of any outside dependency.

What they don't want is the impression of being some kind of pawn in U.S. relations with the Soviets.

Outright American arms sales or a formal military alliance are a long way off in an uncertain future, most experts agree. What the visit of Geng Biao to Washington confirms, however, is that a significant evolution, unthinkable not too many years ago, is plainly under way.