A top White House official yesterday called the Soviet Union "an economic basket case" and said the United States "should not provide the trade and credits necessary to prop up the Soviet economy except in exchange for specific and meaningful Soviet actions that promote stability . . . . "

Thomas C. Reed, who was a consultant to the National Security Council in recent months and yesterday was named a full-time special assistant to the president, gave no details on how such economic pressure on the Soviets would be carried out or what would constitute "meaningful" actions by Moscow.

But Reed's remarks in a speech prepared for delivery before the Armed Forces Communications and Electronics Association last night come as President Reagan faces a difficult decision on whether to lift restrictions barring use of American-made components in equipment being built by West European countries for a Soviet natural gas pipeline.

The president, officials say, is expected to make a decision this weekend. Allies in Western Europe want Reagan to lift the restrictions and some top officials here, including Secretary of State Alexander M. Haig Jr., are said to support this view. Defense Secretary Caspar W. Weinberger and others, however, are said to oppose it, preferring to tighten the economic screws on Moscow as much as possible.

Some White House officials also say privately they are dismayed over the Europeans' failure to adopt a tougher trade policy at the recent economic summit meeting that would have required a substantial Soviet cash down payment for Western equipment and an end to interest subsidies.

Although lacking specifics, Reed's speech illustrates the view of those officials who believe that the United States must take advantage of Moscow's alleged economic weakness.

Writing in The Wall Street Journal on Tuesday, Treasury Secretary Donald T. Regan also suggested that economic pressure would be used in the Strategic Arms Reduction Talks (START) that open in Geneva June 29. The Soviets and their East European allies had better "make some accommodation with us in the field of strategic arms or else watch [their] own weak economies weaken further," he wrote.

Reed claimed the Kremlin had now outstripped this country "by most measures of strategic nuclear power" in the missile field and "within 30 days it can mobilize 200 divisions" on the ground.

But Reed said Moscow also has considerable problems of its own. The Soviet political system, he charged, has lost its "revolutionary zeal." The government "cannot feed its own people" and "the potential for corruption and decay . . . has mushroomed in the dank darkness of the Soviet dictatorship," he said.

Reed also recently directed a White House study of U.S. security policy and yesterday made these key points:

* Although the Joint Chiefs of Staff are known to believe the current administration strategy for countering the Soviets cannot be met with the present five-year, $1.6 trillion budget plan, Reed says "our strategy is to live within" that budget and plan. "We cannot seek more," he said, because the country's economic well-being is also part of the strategy.

The idea, Reed said, is to "put first things first and develop plans for how we will conduct ourselves if worst comes to worst."

* The highest single defense priority is to improve the command and communication systems with which the president would control America's nuclear forces in an atomic war and to improve the chances of survival for the president or his legally designated successors.

"There should be no doubt in the minds of Soviet planners that any attempts to disconnect the national command authorities from control of American weapons in time of crisis will fail," Reed said.

The Reagan administration has made a major financial commitment to improving these functions as a way to convince Moscow that the United States would be able to respond to any first strike. But Reed went on to say that "perhaps for the first time" these functions "are now of direct concern to this president." Actually, former president Jimmy Carter issued presidential directives in 1980 that called for more effective procedures for protecting the president and better command and control over the weapons at his disposal.