U.S. specialists from the National Institutes of Health and the Environmental Protection Administration are scheduled to fly to Moscow today to investigate the effects of a chemical agent the Soviets allegedly used to track the movements and contacts of Americans in their country.

State Department spokesman Charles Redman said yesterday that the two agencies were conducting "a thorough investigation into the implications of exposure" to the "spy dust" used in Moscow and "other tracking agents."

Also yesterday, Undersecretary of State Ronald I. Spiers briefed about 100 diplomats and dependents who had served in Moscow during years when the tracking agent may have been used. Spiers spoke in the same general terms used in earlier briefings to U.S. diplomats in Moscow, telling the group that he had learned about the tracking agent only three days before it was publicly announced last week, according to sources present at the briefing.

Spiers thus becomes the third man who held an important government job in the late 1970s and early 1980s to acknowledge that he had not been told about Soviet use of the chemical, although the government now says that it knew of its existence in those years. Spiers headed the Bureau of Intelligence and Research in the State Department in 1980-81, which allowed him access to sensitive information.

Earlier, former admiral Stansfield Turner, director of the Central Intelligence Agency in the Carter administration, said he had known nothing about the spy dust. And Malcolm Toon, U.S. ambassador to Moscow from 1976 to 1979, said he was told nothing about the dust.

Other government sources said these people were not informed because the Soviets' use of a chemical tracking agent was not taken seriously until this spring. The discovery of a sudden increase in Soviet use of the chemical several months ago plus the finding, also made this spring, that the agent was a "mutagen" capable of altering human genes and perhaps of causing cancer led to the decision to make public statements about the spy dust, officials said.

There were hints from some sources that the United States may have had a tipoff from an intelligence source about Soviet use of the tracking agent.

Senior officials were understood to acknowledge that the timing of the announcement would tend to support charges that the United States was poisoning the atmosphere before the U.S.-Soviet summit scheduled for November in Geneva. The Soviet Union has made such charges since last week's "spy dust" announcement.

But, it was said, officials concluded that the sharply increased Soviet use of the chemical plus the discovery that it could be harmful led to the conclusion that U.S. citizens in Moscow exposed to the spy dust had to be informed. On the theory that such information would quickly leak, the State Department decided to go public from the outset, sources said.

Just how harmful the substance might be remains in doubt. Informed sources said yesterday that some embassy officials in Moscow had developed skin irritations that have been attributed to the chemical, known as nitro phenyl pentadiene aldehyde, or NPPD. However, State Department spokesman Redman said yesterday that "there is no evidence to date that any embassy personnel have suffered ill effects due to exposure to tracking agents."

A chemist who has been a consultant to the Pentagon said that chemical tracking agents have been used for many years by both Soviet and U.S. intelligence and police agencies. Eugene Ashby of the Georgia Institute of Technology in Atlanta said the latest tracking agents are specially synthesized chemicals that can be detected in very low concentrations using laboratory analytic instruments.