The Soviet Union tonight vigorously denied "absurd allegations" that it had used chemical agents to track U.S. officials in Moscow.

The new U.S. charges, which quickly followed a tough speech by national security affairs adviser Robert C. McFarlane and the U.S. decision to test antisatellite weapons in space, were treated in Moscow as part of an effort to undercut preparations for the November U.S.-Soviet summit.

"Behind the raising of this artificial question, one cannot but see a quite definite design -- to prepare the ground for yet another slander campaign against the Soviet Union, to poison the atmosphere in relations between our countries and kindle enmity toward Soviet people," said a Soviet protest note published by the official news agency Tass.

The note, delivered to the U.S. State Department today, said that U.S. claims about the use of possibly harmful tracking chemicals are "not only absolutely out of place but also totally unacceptable."

Read tonight on the evening news program, the note also called the allegations an "act of provocation" and warned that "the American side will bear all responsibility for the possible consequences of actions of this sort."

"It has a very bad smell," said one Soviet observer of what he saw as a turn in Washington's presummit preparations.

Late Thursday afternoon, the ranking Soviet diplomat in Washington, Minister-Counselor Victor F. Isakov, called on Acting Secretary of State John C. Whitehead to deliver a Soviet note on the issue.

Following the meeting the State Department reiterated the U.S. charge and said in a statement, "It is distressing that the Soviets are incapable of facing unpleasant facts in a forthright manner and even more so that they attempted to cover the misdeeds of their officials with accusastions against others."

[The statement said the United States "expects" the dusting to cease forthwith.]

Meanwhile, Americans and western diplomats here were assessing today the evidence about the chemical, nitro phenyl pentadiene aldehyde, or NPPD, a possibly carcinogenic powder allegedly used by the KGB, or Soviet security agency, to track the movements and Soviet contacts of U.S. diplomats and maybe other foreign residents.

Lack of specific information about where the substance was found, how it was known to have been used as a tracking agent and what precautions to take to avoid further exposure heightened skepticism among some members of the foreign community here.

"It seems there are some black holes in the logic," said one western diplomat. Other western envoys who attended a special briefing on the issue at the U.S. Embassy today said they see little cause for alarm.

"The information was put in a nonalarming way," said British diplomat Simon Hemans. "It will be for London to decide what steps need to be taken." He added, "I don't think I am likely to catch anything very fatal continuing to work here."

Today's briefing for diplomats was apparently the same as three held last night at the U.S. ambassador's residence for about 500 members of the American community -- diplomats, journalists, businessmen and family members.

U.S. officials said they have evidence that the dust had been sprinkled on cars and appliances, where it could be picked up and passed on by hand, leaving traces that could be identified later.

They said the tracking agent was first detected several years ago but that its possibly harmful properties were discovered only last year.

No protest was made then because its use was sporadic, the officials said. During spring and summer this year, however, the dust was seen in greater quantities, prompting the letters of protest delivered this week to the Soviet government.

At each of the briefings, Dr. Charles Brodine, flown here from the State Department's medical unit in Washington, said that the health danger, while still undetermined, was probably minimal and no cause for grave alarm.

Nonetheless, some Americans were visibly upset at the revelations and grew more perturbed when they were given no advice on how to protect themselves or their children.

"I want to know what it is I should do," said one young mother. "Should I take my son out of here?"

Richard E. Combs, charge d'affairs at the U.S. Embassy in the absence of Ambassador Arthur Hartman, noted that no one was likely to have ingested the chemical. "The purpose of the KGB here is not to poison people but to assist them in keeping track of people."

Both U.S. officials noted that no final assessment of the health danger could be given until results were obtained by a special team of investigators expected to arrive in Moscow in 10 days.

The reaction to the revelations among most American diplomats was one of concern but hardly panic, said people present at the briefings held for U.S. Embassy staff. "There are a lot worse things," said one embassy staff member today.

According to Dr. Brodine, only three people showed up today at the embassy health clinic to ask him followup questions.

U.S. Embassy officials recalled another scare in the late 1970s, over the harmful effects of microwave radiation beamed at the U.S. Embassy.

The microwave incident also became the topic of headlines at a time when the U.S.-Soviet relationship was worsening. Subsequently, the effects of the microwave radiation were judged by a Johns Hopkins public health school study to be medically insignificant.