A KGB agent's clumsiness in applying too much chemical dust to the steering wheel of a U.S. Embassy car in Moscow last spring tipped off U.S. officials to the extensive use of potentially harmful tracking powder, according to Rep. Daniel A. Mica (D-Fla.).

Mica said he was informed by State Department officials yesterday that the normally invisible "spy dust" turned up as a noticeable yellow powder, apparently because too much was applied, and was spotted by an embassy employe who called it to his superiors' attention.

Mica, chairman of the House Foreign Affairs subcommittee on international operations, quoted Dr. Charles Brodine, a State Department medical specialist, as saying that the KGB agents who secretly planted the chemical dust at U.S. facilities may be facing the most serious health risks from contact with it.

The risks would be greatest if the KGB used aerosol cans and inadvertently inhaled some of the dust, Mica said.

He quoted Brodine as saying that, based on what is known today, the tracking power poses only "a minimal health risk" to Americans who came in contact with it.

Short-term studies of the chemical's effect on laboratory mice, to be completed within two months, may be used to determine whether more serious, long-term studies are warranted.

The State Department physician, who recently returned from discussing the spy dust revelations with U.S. Embassy personnel and other resident Americans in Moscow, was quoted by Mica as saying that if his own wife and children had been exposed to the chemical, he "would not consider it a reason to get out of Moscow."

All U.S. Embassy personnel in the Soviet capital, according to Mica, have been given the opportunity to leave if they are worried that exposure to spy dust will affect their health. But he said none have elected to do so.

"The State Department seems to have notified its employes about the dust and its dangers as quickly as possible," Mica said.

He added that his committee may launch a study to determine if intelligence agencies and other parts of the U.S. government apparatus proceeded as quickly as possible to bring the use of the chemical powder to the attention of high-ranking U.S. officials.