A mild Reagan tries to isolate the Soviets

The United States is genuinely interested in reaching an arms control agreement with the Soviet Union. It supports true nonalignment. And it believes in the United Nations.

These are the three major points President Reagan made as he addressed the 38 th session of the General Assembly of the UN.

Mild in tone, his address Monday was careful not to insult the Soviets directly but nevertheless to criticize them for their handling of the Korean airliner tragedy and alleged violations of arms treaties.

* Geneva arms control talks. With regard to the negotiations over intermediate-range missiles, Mr. Reagan proposed a higher ceiling of missile warheads for each side than he had previously. He accepted the Soviet proposal to include European land-based aircraft of both sides capable of carrying nuclear bombs. He agreed to consider cutting back the number of Pershing II missiles to be deployed in Western Europe if an agreement is reached on overall deployment.

Mr. Reagan's new arms proposals met with mixed reviews here. Some experts believe that by taking another step to meet Soviet concerns about European theater nuclear arms - despite his anger over the Soviets' downing of the Korean airliner - Reagan is showing that he is truly interested in reaching an agreement. Others are skeptical, saying his proposals fall short of what the Soviets can realistically be expected to accept.

''It is no longer a matter of figures and equations,'' a Western diplomat says. ''In the present political climate, Reagan and (Soviet leader Yuri) Andropov cannot be expected to meet. Only at such a meeting can a real breakthrough in the negotiations occur.''

By saying that ''a nuclear war must not be fought and cannot be won,'' Reagan went a long way to dispel his bellicose image. But by making verification a condition to any agreement on arms control, he reduces the chances that such an agreement will be reached.

''Reactions to the Korean airliner tragedy are a timely reminder of just how different the Soviet concept of truth and international cooperation is from that of the rest of the world,'' Mr. Reagan said.

Reagan's sincerity cannot be doubted, but neither are his words likely to entice the Kremlin toward conciliation, observers say.

* Nonalignment. The President said the US approves of nonalignment when nations want to avoid taking sides between East and West. But some ''nonaligned'' nations are client states of the USSR and contribute to polarization of the UN, he said.

The President said the West is not a bloc. In fact, he strongly hinted the West and the third world are natural allies, while the communist-bloc countries are the troublemakers.

But there is no indication that most third-world countries will be convinced that they are ''natural allies'' of the West, any more than they were convinced yesterday by Moscow's contention that they are ''natural allies'' of the communists.

* The United Nations. Mr. Reagan went a long way to praise the UN and to underline American commitment to it, to its Charter, and to its efforts. ''We give our unwavering support to the peacekeeping efforts of this body,'' he said, and he stressed that ''the UN has a proud history of promoting conciliation and helping keep the peace.''

Reagan's speech ''broke no dramatic new ground,'' says an analyst. ''But it was . . .probably effective in the sense that it aimed at drawing a wedge between the UN (and) the majority of its members on the one hand, (and) the USSR on the other.''