Riddle: what goes up while it goes down?

Answer, as supplied yesterday by the State Department after a protest from Peking: U.S. arms sales to Taiwan.

The reason for the discrepancy, as explained by State Department spokesman Alan Romberg, is that the Reagan administration has applied indexing to its Taiwan arms sales to account for inflation.

In a joint U.S.-China communique intended to settle differences on this contentious question, Washington agreed last Aug. 17 that its arms sales to Taiwan would not exceed "the level of those supplied in recent years" either in quality or quantity. Instead, the United States promised to "reduce gradually" the level of its sales, "leading over a period of time to a final resolution."

Since the signing of the communique, U.S. officials have refused steadfastly to specify ceilings they planned to apply to arms sales to Taiwan. But early this month they were required by law to submit projections to Congress covering sales for the next two years.

According to that "congressional presentation document," the United States expects in fiscal 1983 to sign contracts with Taiwan for $700 million in arms or military services while $100 million in other commercial arms is exported.

In the following year, fiscal 1984, the arms supply level is expected to drop slightly to $780 million worth, the document said.

These figures are well above the $600 million total transactions for fiscal 1982 and far above the unusually low level of $295 million recorded in fiscal 1981.

On hearing of the new projections, the Chinese Foreign Ministry lodged a protest with U.S. Ambassador Arthur W. Hummel Jr. last Thursday. Yesterday, Chinese officials made their displeasure public in a Foreign Ministry statement charging that the planned U.S. arms sales level "greatly exceeds" the level of recent years and violates last August's communique.

Romberg, in reply, said the new projections are "fully consistent" with U.S. promises. To illustrate, he reached back to fiscal year 1979, when U.S. arms sales to Taiwan were $598 million, and said that would be equivalent to $830 million in current, inflated dollars.

The State Department also seemed to open the possibility of even higher levels by saying that "although there may be occasional fluctuations," a downward trend will be apparent over time.

Another explanation offered by the State Department was that U.S. arms sales to Taiwan were held to "extremely low levels" in fiscal 1982, while last August's communique was under negotiation.

While the long-running Sino-American dispute emerged anew, Chinese and Soviet officials were meeting in Moscow to discuss improvements in relations.

A new and unwelcome factor in the Taiwan tangle, as seen by Peking, was the recent introduction by prominent U.S. lawmakers of resolutions calling for settlement of Taiwan's future to be "acceptable to the people of Taiwan."

Two of the resolution's sponsors, Sens. Claiborne Pell (D-R.I.) and John Glenn (D-Ohio), said they had in mind the 16 million native-born Taiwanese rather than the 2 million Chinese who fled the mainland with Chiang Kai-shek in 1949 and who hold most of the power on Taiwan today.

A commentary last week in Peoples Daily, the newspaper of the Chinese Communist Party, called the resolution "crude interference in China's internal affairs."