MOSCOW (AP) _ A Soviet official has called on Americans to express support for a U.S. scientist fasting for disarmament, saying ''it is wrong to sit back and wait for this noble man to die.''

Georgy Arbatov, head of the U.S.A.-Canada Institute and a member of the Communist Party Central Committee, on Wednesday said Charles Hyder's five- month hunger strike had aroused great concern among many Soviets.

Hyder, 56, a former NASA astrophysicist, has been fasting in Washington's Lafayette Park across from the White House since Sept. 23 to call for the dismantling of all U.S. nuclear warheads by the year 2000.

Soviet leader Mikhail S. Gorbachev appealed to Hyder last week to cease his fast, but Hyder refused. Soviet media have given the fast near-daily coverage, and Hyder frequently is interviewed on state-run television.

In an open letter distributed to reporters in Moscow, Arbatov wrote: ''I urge you to do whatever you can. It is wrong to sit back and wait for this noble man to die.''