The United States and the Soviet Union traded charges yesterday about interference in Iran, amid deepening concern among Washington policymakers that the shah's moment of decision is at hand.

Interagency planning for "worst case" outcomes has been stepped up, including contingency plans for evacuating the 35,000 Americans there and extracting or disabling the supersonic warplanes and other highly advanced U.S. military equipment supplied to the shah. State Department officials denied, however, that there has been a sudden acceleration of these plans.

Pentagon officials said the military judgment as of now is that security is adequate to protect U.S. military equipment and intelligence-gathering gear in Iran. The safety of Americans and security of the equipment are reported to be under review by a National Security Council subcommittee headed by presidential assistant David Aaron and an Interagency Task Force headed by Undersecretary of State David D. Newsom.

Serious consideration is being given to the dispatch of a U.S. Navy carrier task force to the Persia Gulf to show the flag and underscore U.S. warnings against "external forces" intervening in Iran, according to official sources. The sources said, however, that no decision has been made and no orders have been issued.

High U.S. officials said they have no indication that the Soviet Union is playing a major role in the still-growing Iranian tumult. However, the officials noted that the Soviets have stepped up their radio broadcasts to Iran and are taking a much harsher tone against both the United States and the shah.

A Soviet charge of American interference, published in the Communist Party newspaper Pravda, prompted a rare U.S. countercharge against the Soviet Union regarding Iranian matters.

The Pravda article, also distributed by Tass, the official news agency, charged that "a special American group" of 60 officials of the CIA, State Department and other agencies has landed in Iran to find ways to keep the shah in power. The article charged that the team is looking for politicians who can be included in a new govenment under the shah to accommodate the interests of "the American oil and military monopolies."

Pravda said "such interference is inadmissible" and that "the events in Iran are purely an internal matter... [which] should be settled by the Iranians themselves."

State Department spokesman Hodding Carter denounced Pravda's "special group" report as "false." Carter added that, "at this point, we find false reports by the Soviet Union to be clearly unhelpful at a time when there is a need to calm the passions and not to excite them."

Frior to a public warning against foreign interference in Iran on Nov. 19 by Soviet leader Leonid Brezhnev Moscow's press and propaganda organs had little to say about the unrest in its neighbor country.Brezhnev's statement, which cast the Soviet Union as the protector of Iranian integrity, was followed by an increase in the press reporting and the beginning of Soviet broadcasts in Persian which attacked U.S. influence and praised insurgent forces against the shah.

Soviet broadcasts to Iran have stepped up again since mid-December, according to American officials. Recently these broadcasts have charged that "United States imperialists are shamelessly interfering with the internal affairs of Iran" and blamed U.S. interests for corruption, inflation and other ills.

Recent Soviet commentaries were based in large part on selective quotations from Western news media, and many of the accounts were datelined New York, in an evident attempt to shield the Soviet Union from charges of direct involvement.

For the first time yesterday, a Moscow radio broadcast in Persian to Iran quoted accounts of the Pravda correspondent on the scene in describbing "mass anti-government and anti-U.S. demonstrations." The broadcast, addressed to "dear listeners," was one of a nearly daily series in this vein.

State Department spokesman Carter yesterday reaffirmed U.S. support for the shah "in whatever he under-takes" to restore stability. Privately, some American officials are saying that the deepening crisis is bringing a moment of decision for the monarch, with his fate depending on events of the next several days.

It is far from clear that dispatch of a naval carrier force would have much effect on the political situation in Tehran. Such a U.S. military movement was proposed and rejected several weeks ago.

If a carrier and its escorts were ordered to the Persian Gulf, they probably would have to come from the 7th Fleet in the Pacific, according to military sources.