Soviet Foreign Minister Andrei Gromyko today dismissed President Reagan's new arms proposals as "patently unacceptable" and accused the United States of blocking negotiations on reducing nuclear weapons.

In the first high-level Soviet reaction to Reagan's speech Monday to the United Nations General Assembly, Gromyko said that the United States and its West European allies had rejected the principles of equality and equal security.

He reiterated a Soviet threat to take "countermeasures" if Washington deploys cruise and Pershing II missiles in Western Europe as planned this year.

Gromyko, who cancelled plans to address the General Assembly after his plane was barred from landing at civilian airports in the New York area, was speaking at a luncheon for Czechoslovak Foreign Minister Bohuslav Chnoupek.

The critical tone of Soviet commentaries on Reagan's arms proposals appeared to rule out any early breakthrough in the Geneva talks on limiting intermediate-range nuclear forces. Western diplomats noted, however, that Soviet commentators had refrained from responding directly to the detailed changes in the U.S. negotiating position.

In a report from New York, the official Soviet news agency Tass said that Reagan had been "deliberately vague," had "kept things back," and had "made omissions" in his speech. This formula suggests that, while the Kremlin's initial reaction to the speech is negative, Soviet leaders are anxious to explore some of the specific elements.

The Soviet media still have not reported the substance of Reagan's offer to include nuclear bombers in calculations of medium-range weapons systems. This has been one of the Kremlin's longstanding demands. Neither have Soviet reports mentioned Reagan's suggestion that the United States might agree not to match global levels of Soviet intermediate-range warheads.

Instead, official Soviet commentaries have concentrated on the obstacles to any agreement. One is the Kremlin's insistence that it be allowed to offset 162 French and British nuclear missiles with its own medium-range SS20 force.

The Soviets also assert that stationing U.S. nuclear missiles in Western Europe would upset the East-West balance.

Soviet commentators have accused Washington of seeking to regain nuclear superiority. In a clear reference to Reagan's U.N. address, Gromyko said that the United States and its allies have kept turning their back on "the principle of equality and equal security, putting forward lopsided proposals patently unacceptable to the other side."

The Tass report from New York described Reagan's proposals as "a propaganda game" and "verbiage" intended to camouflage "the unrestrained buildup of U.S. armaments for conducting nuclear war."

Another Tass commentary expressed surprise at the fact that the president "used the word detente without an abusive epithet for the first time in 10 years."

Tass said that Reagan took care not to address the U.N. General Assembly as if it were a Republican Party convention--but expressed doubt over whether the change in rhetoric was genuine or a "propaganda facelift" by the president's advisers.