The new Soviet leadership indicated today that it expects some concrete American moves to ease tensions before taking up President Reagan's offer to seek a "more constructive relationship."

The Kremlin's top expert on U.S. affairs, Georgy Arbatov, said Reagan's recent gestures have "raised new hopes . . . that things could move in a positive direction." But he said the question in Moscow is whether "this is only a maneuver to calm down the public in order to continue the same policy" that Reagan has pursued during the past 21 months. "We don't have an answer," he added.

Arbatov suggested that the Soviets were on the threshold of a decision to escalate the arms race to counter what he called an "unprecedented" American arms buildup. He quoted Leonid Brezhnev as saying "shortly before his death that 'We are at a crossroads and we have to decide which way to go'."

Well-informed Soviet sources said the new leadership has suspended for the next couple of months what was forecast by Brezhnev as a major counteroffensive in the fields of propaganda and weapons development, one that would undoubtedly have pushed Soviet-American relations into an even sharper confrontation.

Arbatov, who has close personal ties to the new Communist Party chief, Yuri Andropov, reaffirmed Soviet desire to "normalize" U.S. relations. Speaking at a meeting of the Soviet-American Trade Council, he asserted that Reagan's conditions, "asking for capitulation," cast doubts on his sincerity. "We are not going to take this. We are not going to buy Reagan's smile with the betrayal of our friends. We are not going to start unilateral disarmament because, as a payment, they have started to talk to us in a civilized manner--as they should anyway," he said. "We are carefully weighing each sign" from Washington for "something concrete" to suggest a change of course.

Arbatov heads the Institute of the United States and Canada.

In the audience were more than 250 American businessmen, including chief executives of Armco Inc., Dow Chemical, Cargill, Stauffer Chemical, FMC Corp. and Occidental Petroleum, along with members of a congressional delegation and U.S. Ambassador Arthur Hartman.

The Americans have presented the Soviets with an extensive list of items that can be exported to the Soviet Union, including food-processing machinery, agricultural equipment, power generation and distribution equipment, chemicals, metals, minerals, natural and synthetic rubber, electronics and machine tools.

Hartman told the council meeting, nominally annual but suspended for the past three years, "We believe all these areas will permit a wide variety of trade to proceed in years to come."

Soviet Foreign Trade Minister Nikolai Patolichev said in his speech to the group yesterday that trade could develop only if "the United States once and for all" renounces the use of trade "as a weapon against our country." Without such measures to generate confidence, "no businessman will sign a deal," he added.

Georgy Kornienko, the first deputy foreign minister, also addressed the group yesterday at a Kremlin lunch. He seemed far harsher than Arbatov, calling U.S. positions in Geneva arms control negotiations "illogical" and attacking Secretary of Defense Caspar W. Weinberger.

Arbatov, on trade, said Moscow had hoped that "it would create the foundation of confidence" and that "unfortunately" the American use of sanctions and embargos has turned trade into "a confidence-destroying measure."

But, he said, "we think there is no alternative to coexistence" and there are signs "that something is changing." He cited the lifting of sanctions on sales for the Siberian gas pipeline, Reagan's decision to send a high-level delegation to Brezhnev's funeral and Reagan's personal gesture of visiting the Soviet Embassy in Washington last Saturday.

Arbatov said it was "hypocritical" to talk about human rights in the Soviet Bloc. "Why don't you talk to Turkey, Chile or Pakistan, why don't you do something about human rights there?" When Washington raises the Afghanistan issue, "we can talk about El Salvador," he added.

In what seemed to be a direct appeal to the businessmen, Arbatov said that something must be done to improve relations since "the alternative does not exist."

He quoted from a Soviet writer who said, "Don't fear your enemy, for he can only kill you. Don't fear your friend, for he can only betray you. But fear those who are indifferent, because their indifference creates the situation in which the killings and betrayals can take place."

In an apparent allusion to recent improvements in Sino-Soviet relations, Arbatov quoted a Mao Tse-tung saying to back up his argument that both the Americans and Soviets should make a solid effort to "normalize" relations and that the "current situation is not going to change unless we change it."

Mao, he said, declared "the table will not move unless it is moved." This is believed to be the first time Mao has been cited with approval in a public meeting in Moscow in 20 years.

In another indication of thaw in Sino-Soviet relations, Chinese Foreign Minister Huang Hua was given a dinner tonight by Deputy Foreign Minister Leonid Ilyichov.