The Soviet Union and the United States, on the eve of their first high-level talks of the Reagan administration, today exchanged harsh charges which dramatized growing East-West tensions along a broad front.

The Soviet charges by Foreign Minister Andrei Gromyko in a lengthy, caustic and sometimes sarcastic address to the United Nations General Assembly, was a head-on attack on recent U.S. policies and a notable departure from the relatively restrained official Soviet rhetoric of the past nine months.

The U.S. positions, in a letter from President Reagan to Soviet President Leonid Brezhnev delivered today in Moscow and made known here in paraphrase by a U.S. spokesman, were less provocatively stated. But they nonetheless included strong charges and accusatory language which is rare in a letter between powerful heads of state.

The day's exchanges and events created an atmosphere of pessimism for the meeting here Wednesday afternoon between Gromyko and Secretary of State Alexander M. Haig, Jr. The session and an additional meeting scheduled for Monday are expected to set the tone and perhaps the terms for the official Soviet-American dialogue in months to come.

The one tangible agreement now anticipated from the Haig-Gromyko meetings is an announcement of the time and place for a start on full-scale Soviet-American negotiations on the limitation of medium-range nuclear missiles in Europe. Both Gromyko's speech and Reagan's letter expressed a desire to move ahead to such negotiations, but this was heavily qualified in both cases by statements reflecting contrasting views.

Reagan, while hoping for agreement, charged that the Soviets "upset" the nuclear balance in Europe by "an unprecedented buildup" of SS20 medium-range missiles, according to the rendition of the U.S. president's letter made public by State Department spokesman Dean Fischer.

Gromyko rejected in advance "linkages" between arms control negotiations and regional conflicts, saying "nothing will come" of such bargaining. This linkage has been a key point of the Reagan administration's policy.

Moreover, Gromyko, while saying that the medium-range missile talks "will apparently be resumed," called for "concurrent settlement" of questions about other "forward-based systems" such as older missiles and carrier-based aircraft. The United States does not favor including these in the talks.

The Soviet foreign minister's 75-minute address was predominantly devoted to a litany of charges against the United States mentioning just about every region of the world and nearly every area of East-West controversy.

Among other things Gromyko charged Washington with "hostile, criminal intrigues against Cuba," superintending the massacres of "thousands of civilians" in El Salvador, "shameless pressure" and "armed provocation" agai.nst. Libya, cooperation with "hegemonism and aggression" by China in a manner "openly hostile" to the Soviet Union, waging "an undeclared war" against the government of Afghanistan, and "direct assistance" to South African "racists."

Gromyko charged that the U.S. rapid deployment force, "regarded in Washington as a great invention . . . is nothing but a policeman's billy stick intended to ensure crude interference by the United States in the affairs of independent states and to stifle the freedom of peoples."

He called for the U.S. "naval armada" in the Persian Gulf to leave the area, saying it is directed against Iran and the Soviet Union but "there is nothing for it to do there, nothing to defend."

Perhaps the most basic charge in Gromyko's broadside was that Washington was implementing a fundamental reversal of previous U.S.-Soviet understandings by "reneging" on the unratified SALT agreement, beginning a "huge increase" in arms spending "such as history has never known" and seeking "military superiority" over the Soviet Union.

Nonetheless, Gromyko declared and repeated for emphasis, "the Soviet Union has not sought, nor is it seeking, confrontation with the United States of America. It would like to have normal businesslike relations with the United States."

In what seemed to be a bid for international public opinion, especially in the political battlegrounds of Europe and the Third World, Gromyko portrayed the Soviet Union as an innocent and injured party which continues to seek peace against all rebuffs.

His one new proposal was that the General Assembly adopt a resolution condemning states, leaders and doctrines that call for the "first use" of nuclear weapons. In the past the United States has refused to renounce the possibility of using such weapons first on grounds this would undermine military flexibility and deterrence.

State Department spokesman Fischer said Haig viewed Gromyko's speech as "disappointing . . . extremely defensive in tone."

One topic Gromyko handled with relatively little bombast was Poland, the most tense and delicate East-West concern at present. The Soviet foreign minister said, "A lot is being done to shake loose the socialist foundations of the Polish state" and charged that "certain quarters" in the West are seeking to interfere in Polish affairs. Beyond this he contented himself with repeating a Warsaw Pact declaration that Poland "is and will remain a socialist state." Reagan's letter to Brezhnev, as described by Fischer, said the United States is "highly concerned" about the situation in Poland and outside interference there "would have serious consequences for all of us."

Haig, meeting Polish Foreign Minister Jozef Czyrek early today, said "the United States wants to be supportive but will not interfere, and expects others to do the same," according to Fischer. The spokesman said additional U.S. aid to Poland was under study.

According to U.S. officials here, Reagan's letter was approved by him and dispatched to Moscow on Monday and delivered by a U.S. Embassy official there this morning, in an effort to "influence the atmosphere" for the Haig-Gromyko talks. Officials said the letter had been in preparation for more than two weeks.