A senior western diplomat here said today it was unlikely that the Soviet security agency KGB knew that the chemical compound it was using to track U.S. Embassy personnel was a potential health threat.

"The supposition is that the KGB did not know," the informed diplomat said, noting that the protest over the use of the chemical tracking agent was made public to warn the American community here.

The State Department's failure to inform the American community here promptly about possible microwave radiation hazards more than a decade ago led to this week's hurried announcement about the use of NPPD, as the chemical is called, the diplomat said.

The experience at the U.S. Embassy here in the early 1970s left "a very strong feeling" among embassy personnel, the diplomat said.

Microwave beams were directed at the embassy for more than a decade and had long been monitored by U.S. personnel under tight security wraps before embassy personnel were officially informed in 1976.

An outcry ensued as Foreign Service groups, newspaper writers and others blasted the government for putting U.S.-Soviet relations above the health of its employes.

"In light of that, largely, and perhaps for other reasons, when dealing with this problem, it was decided to go ahead," the diplomat said. "It was a judgment call."

Richard E. Combs, charge d'affaires at the embassy, told members of the U.S. community here Wednesday that he had only been informed of the warnings about NPPD last weekend.

Dr. Charles Brodine, assistant medical director of an environmental health unit at the State Department, also said he was only informed of the situation over the weekend, and was rushed to Moscow with only two hours' sleep in the previous 36 hours.

The urgency with which the warning about the chemical dust was delivered has prompted skepticism among some members of the western community here about the motives of the American announcement.

U.S. officials have said that the use of chemical tracking agents by the KGB has been known since 1976 and that NPPD was proved to be a mutagen -- an agent causing changes in genes, in some cases leading to cancer -- last year. However, no protest was lodged with the Soviets either over the use of tracking agents -- presumably used to monitor contacts between U.S. diplomats and Soviet citizens -- or over the potential health hazard of NPPD until this week.

U.S. officials have said that evidence that NPPD was being used increasingly during the spring and summer led to this week's warning.

The senior western diplomat said the potentially harmful aspects of NPPD had not been brought up in any U.S.-Soviet conversation that he was aware of.

The microwave controversy had been brought up privately with the Soviets in 1967 and 1969, long before the issue was made public in 1976. However, the beaming of the microwaves did not cease until 1977, after the public protest. It was resumed again in 1979, and again in 1983, each time only briefly. The microwaves were allegedly used to block U.S. interception of Soviet radio transmissions.

In the meantime, several U.S. employes had filed compensation claims. A statistical study carried out by Johns Hopkins University later showed that the radiation had no discernible health effect.

U.S. officials have given no examples of how NPPD -- formally, nitro phenyl pentadiene aldehyde -- was discovered, saying only that it had involved U.S. diplomatic personnel in Moscow and Leningrad.

The senior diplomat said a team of U.S. experts expected to arrive here next week should have no trouble tracking the compound, since it apparently lingers on natural fibers and on skin -- unless washed off with alcohol-based soap.

The Soviet government newspaper Izvestia said tonight that the charges about NPPD were the work of those trying to derail the U.S.-Soviet summit meeting scheduled for November.

"It is as if someone in the U.S. is not keen that Soviet-American relations travel the path of normalization," Izvestia said.

The senior western diplomat said the Soviet denial of the charges was to be expected. "It would be quite surprising if taken any other way," he said.