Soviet Defense Minister Marshal Dmitri Ustinov issued a veiled warning today that the Soviet Union may adopt a defense posture providing for an almost instant retaliatory nuclear strike if monitoring equipment detects a U.S. attack.

It was difficult to determine whether Ustinov's warning was designed to frighten the American public and increase psychological pressure on the Reagan administration in response to its arms buildup, or whether a policy of "launch on warning" was actually being considered as a serious option.

In a detailed and very pessimistic article that took up an entire page of the official party newspaper Pravda, Ustinov asserted that Reagan's actions "in their totality" have led Moscow to the conclusion that his objective was to destroy socialism.

Yet Ustinov defended the Kremlin's "peace policy" and particularly the recent pledge not to use nuclear weapons first. He said it did not diminish Soviet security in any way.

Despite Reagan's strategic buildup, he said, the United States will not be able to wage a victorious nuclear war against the Soviet Union. Ustinov asserted that the Soviet government would meet "a sharp demand" for greater combat readiness of its forces and for modern command and control systems and "other technological means."

Ustinov said there should be a clear realization in Washington and other Western capitals "that by renouncing the first use of nuclear weapons, the Soviet Union also denies this to all who are hatching plans of a nuclear attack."

"The aggressor, too, should know that the advantages of the preemptive use of nuclear weapons will not ensure victory for it. In perpetrating a crime against humanity it will not gain sizable benefits. With the current state of the systems of detection, the combat readiness of the Soviet Union's strategic nuclear means, the United States will not be able to deal a crippling blow to the socialist countries. The aggressor will not be able to evade an all-crushing retaliatory strike," Ustinov said.

Ustinov's words were interpreted by Western military experts here as a hint of what Soviet officials have told visiting Americans about the possible Soviet response to the introduction of medium-range Pershing II rockets in Western Europe.

In contrast to the policy of "launch under attack," the Russians have said that the proximity of the Pershings would force them to switch to "launch on warning."

Ustinov's article appeared to have been designed for the domestic audience, suggesting worries within the armed forces and perhaps the population as a whole about the government's "peace policy," which does not seem to be going anywhere.

In language that suggested an internal debate over defense policies here, he said that "the Soviet people, our friends," have been "asking questions whether the right moment has been chosen for" the pledge of no first use of nuclear weapons "and whether by the unilateral commitment we are not incurring excessive danger upon our people, our homeland and the cause of socialism."

Soviet sources privately interpreting Ustinov's article said that Moscow intends to develop "an early-warning system of the highest quality" and also test the use of a laser "shield" against incoming rockets and cruise missiles. The sources insisted that no new nuclear-weapons system is being contemplated.

Ustinov said that "it is necessary that the influence of the factor of surprise be reduced to a minimum so that the aggressor should not be tempted to use with impunity its nuclear weapons first."

The Soviet Union, he said, "will further build its policy and maintain its defense capacity considering the behavior of the United States." Knowing the "aggressive" character of U.S. policy, the marshal said, "our defensive military doctrine will not be of a passive character."

Ustinov's conclusions were preceded by a detailed indictment of Reagan's economic, foreign and military policies. He listed new U.S. weapons programs that, he said, would give Washington "a first-strike potential." He assessed the scheduled deployment of 572 nuclear weapons in Western Europe next year as an effort to cut the distance "from which to make such strikes."

Then he analyzed what he called Reagan's "doctrine of confrontation" and his quest for military superiority. Linked to military measures are political, economic and propaganda measures against socialist states," he said.

Ustinov cited attempts to mount a trade, credit and technological "war" "aimed at creating prerequisites for a fight to destroy socialism as a socio-political system."

Ustinov charged that the United States had put in "high gear its machinery of destruction." When high U.S. officials talk of "their potential enemy," he asked, should Russians go to bed every night fearing the possible use of nuclear weapons?

"The threats used by the Reagan administration, its arbitrariness which is called unpredictability, are not just words. Behind them are mountains of arms and programs for the production of new, still more destructive armaments and directives for using them."

He made clear that there has been no progress at the Soviet-American talks in Geneva on reducing nuclear arms in Europe. The impression is growing, he said, "that the United States does not intend to make constructive steps in" these negotiations.

Ustinov described Reagan's "zero option" proposal for the European missile talks--eliminating both sides' intermediate-range, Europe-based missiles, as a call for Soviet disarmament, adding, "I would like to make it clear that the Soviet Union will not embark on unilateral disarmament."

Ustinov also expressed deep skepticism about U.S. intentions at the strategic arms talks in Geneva and underscored Soviet determination to maintain and preserve "everything positive" achieved in the previous SALT negotiations.

He specifically denounced as "malicious lies" Western charges that the Soviet Union has continued to deploy its SS20 medium-range nuclear missiles despite the announced unilateral freeze on their deployment.

Despite Reagan's policies and programs, Ustinov asserted, the United States will not be able to gain "military superiority either at the stage of preparing a nuclear war or at the moment when they try to start that war."