The Soviet Union, in an unusual move reflecting the embittered state of superpower relations, yesterday made public its first substantive diplomatic communication with the Reagan administration, charging the United States with "open interference" in Poland and other antagonistic acts.

State Department officials said the public release of Foreign Minister Andrei A. Gromyko's Jan. 28 letter to Secretary of State Alexander M. Haig Jr. was unprecedented in the recent history of Soviet-American exchanges. The officials said they were puzzled by the action, especially because Moscow has usually placed great importance on confidentiality and proper form in its diplomatic exchanges.

The Soviet Embassy, in releasing Gromyko's letter, said it was doing so because Haig's part of the exchange "has been made public by the U.S. side." bAlthough there have been Washington news reports revealing that the new secretary of state sent a Jan. 24 letter to Gromyko and describing its nature in general terms, State Department officials denied that the U.S. communication was made public.

The State Department declined to disclose its side of the exchange and had no official comment last night on the Soviet action.

The Soviet letter contained some strong language, including accusations that "tendentious assessments" and "distorted interpretations" have been aimed at Moscow regarding Iran, that U.S.-controlled radios have made "provocative and instigatory" broadcasts to Poland, and that the United States continues to "raise obstacles" to a diplomatic dialogue aimed at Soviet withdrawal from Afghanistan.

Nonetheless, it was not so much the tone or substance of the letter as the fact of its publication that raised eyebrows in Washington. The State Department was notified of its release by the Soviet Embassy only a few minutes before it was supplied to American news organizations.

Haig's letter to Gromyko, delivered through the U.S. Embassy in Moscow, was the opening missive in the official relations between the two countries. Gromyko's reply was delivered to Haig by Soviet Ambassador Anatoliy Dobrynin in the call made famous by the U.S. decision that he could no longer use the basement garage of the State Department to arrive unseen on confidential business, but must use the front door like other ambassadors.

Both Haig's letter and Gromyko's reply came after many preinauguration statements by Ronald Reagan and Haig expressing disapproval and dismay at Soviet activities throughout the world, but before Reagan's public declarations from the White House that the Soviets will cheat, lie and "commit any crime" to support world revolution, and before Haig's news conference charge that the Russians "foster, support and expand" international terrorism.

According to U.S. sources, Haig's letter, like Gromyko's reply, dealt principally with three areas of contention and cross-purposes in Soviet-American relations of recent months: Iran, Poland and Afghanistan. s

Beginning with a stiff protest by then-Secretary of State Edmund S. Muskie in the final weekend of the Carter administration and continuing into the early days of the Reagan administration, the United States denounced Soviet press and radio reports regarding the U.S. hostages in Iran.

In the U.S. view, Soviet charges that the United States was preparing to attack Iran provided arguments that Iranian factions might use in opposing the hostages' release, and charges that the United States was brainwashing the released hostages seemed calculated to curry favor with their former captors in Tehran.

Gromyko, in his letter, said the Soviet Union "in clear and unambiguous terms" opposed the taking of the American diplomats as hostages, and said that "the U.S. government is also fully aware . . . that we addressed ourselves directly to the Iranian leadership on the issue."

The Soviet foreign minister pointed out that the Soviets cooperated in the United Nations condemnation of Iran for the hostage-taking, but he did not mention that the Russians subsequently vetoed binding sanctions against Iran proposed by the United States.

In a tone more of sorrow than of anger, Gromyko wrote Haig that "neither your letter, nor the public statements of the officials of the administration contain a single kind word addressed to the Soviet Union in connection with the position it adopted." Instead, he charged, "clearly tendentious assessments" of Soviet news media reports were released "to entirely distort" the Soviet position in public eyes.

"One cannot help asking a question for what reason all this is being done," Gromyko wrote.

Both the Carter and Reagan administrations have warned Moscow that a Soviet invasion of Poland would have "the gravest consequences" for East-West relations. Many U.S. assessments of Soviet military readiness on the Polish borders have been made public.

The most recent U.S. position, expressed by the State Department Tuesday and repeated yesterday, is that a Soviet invasion of Poland is not imminent, inevitable or justified on any grounds. State Department spokesman William Dyess again denied press reports that Haig considers such a Soviet action inevitable, saying that the opposite view is the authorized position of Haig, the State Department and the U.S. government as a whole.

Gromyko charged in his letter that "provocative and instigatory transmissions" to Poland of the Voice of America and other radio stations under U.S. control constitute "an open interference in the Polish internal affairs . . . aimed at generating among the Polish population unfriendly sentiments with regard to the Soviet Union." U.S. officials have denied charges that the broadcasts are inflammatory.

Gromyko also referred without elaboration to other "facts" which indicate that Western "interference" in Polish affairs is not limited to the broadcasts.

Gromyko, in summary, asked what purpose is served by introduction of "the Polish topic" into the Soviet-American dialogue and he complained of "inappropriate warnings" addressed to the Soviet Union.

Many U.S. statements to and about the Soviet Union in the past 14 months have roundly condemned the Soviet invasion of Afghanistan, and U.S.-backed international sanctions sought to penalize the Soviets for the invasion and pressure them to withdraw.

Gromyko repeated the longstanding Soviet position that "armed incursions" and "all other interference" in Afghan internal affairs be terminated as a first step toward Soviet withdrawal.

The Soviet official said that the United States could contribute to a political settlement by facilitating a dialogue between Afghanistan and Pakistan but that Washington, instead, attempts "to raise obstacles" to such discussions. Pakistan, with backing from the United States as well as most Islamic countries, has refused direct discussions with the Soviet-installed Afghan government of Babrak Karmal because this would imply its international acceptance and recognition.