Gen. Alexander Haig, the top U.S. and NATO commander in Europe, said last night that he sees no evidence, "not one iota," that the Soviets are exercising restraint in what he called "their ongoing nuclear and conventional" weapons buildup.

President Carter, in a decision last April that stirred considerable controversy within the North Atlantic alliance, decided to defer production of U.S.-developed neutron warheads. The president explained at the time that a final decision eventually would "be influenced by the degree to which the Soviet Union shows restraint in its conventional and nuclear arms programs and force deployments affecting the security of the U.S. and Western Europe."

"As you know," Haig told a gathering of the prestigious German Foreign Policy Society here, "we are now in a hiatus period, a period of so-called non-decision" with respect to the neutron warheads in which "assessments are under way of compensatory restraint by the Soviet Union.

"I must say if you ask me do I see any evidence, I would suggest not one iota," Haig said.

Haig made his comments during a question and answer session after an informal speech to several hundred invited guests. Throughout his talk, Haig repeatedly stressed what he views as menacing growth of Soviet might and its use on a global scale, frequently outside areas of NATO responsibility.

Referring to Soviet front-line strength, he said the idea that "the next conflict may turn out to be a come-as-you-are-party," - a reference to short warning - "may not be so wrong."

He chided analysts who attribute the Soviet military buildup to a Russian military-industrial complex that is out of control. He attacked the view that "because it is mindless it is therefore benign. Rather," he said, "no rational analysis supports that view," adding that the Soviet buildup, in his opinion, was providing new military hardware "in a balanced way."

When a questioner suggested that the Soviets actually had done rather poorly in several countries where they have tried to intervene, Haig countered that the West could not always count on that happening and that there were places, in Africa and near the Persian Gulf, where the Soviets had done well.

The general, in his speech and under questioning, also sought to warn Europeans against thinking that U.S.-developed cruise missiles - small jet-powered missiles - are the answer to all future problems. He suggested Europeans are building these weapons up to much as the answer to new Soviet threats.

Haig told a questioner that the regional balance of forces in central Europe today is "a very sensitive question" and that the balance is "in jeopardy" because of new Soviet SS-20 medium-range missiles, Backfire bombers and long-range naval aviation.

But he pointed out the cruise missiles reach their targets very slowly - flying at jet airplane speeds - and that the key Soviet threat against Europe comes from a ballistic missile, "instantaneous" rocket power of the SS-20.

Haig was suggesting that adding to or modernizing the West's ballistic missiles on land, at sea and in the air also should be considered. Because, he said, if the West wants to deter any attack, counter it, or negotiate it out of existence, more than just cruise missiles is needed.