Defense Secretary Richard B. Cheney has ordered 40,000 U.S. troops pulled out of Europe over the next year, according to an announcement released yesterday.

Cheney said the troop reductions would be made in conjunction with the anticipated agreement on conventional arms control with the Soviet Union by the end of this year.

"We have to begin the drawdown now to respond in an orderly way to changing security requirements and declining defense budgets," Cheney said in a statement.

The United States now has about 300,000 military men and women stationed in Europe. Under proposals now under consideration at conventional arms talks in Vienna, the United States and Soviet Union would each eventually cut their force levels to 195,000.

The Senate, seeking even sharper reductions than Cheney's, has called for the withdrawal of 50,000 U.S. troops from Europe.

Cheney said the cuts would include 30,000 Army forces and 10,000 Air Force personnel.

"Although the personnel drawdown will begin in October, no units will be deactivated before Jan. 1, 1991, to allow the affected units planning time and to avoid placing excessive strain on the logistics system," the Defense Department said in a statement yesterday.

On the issue of the Soviet military, the Defense Department has published a new assessment of the Soviet military threat that struggles to balance the traditional Pentagon views of a muscular Soviet military with the historic political and economic upheaval of the past year in the Soviet Union.

"This document will not please either those who believe that the Soviet threat has completely faded away, or to those who say it is largely unchanged," Pentagon spokesman Pete Williams said Tuesday in describing this year's 111-page "Soviet Military Power."

But even Cheney, who ordered that the Pentagon continue producing the document for a ninth year despite the radical changes in the Soviet Union, shied away from this year's presentation. For the first time since former defense secretary Caspar W. Weinberger created "Soviet Military Power," the defense chief who signed the review did not unveil it to the news media.

"He {Cheney} thinks it's important for us to put it out," said Williams. "But there are some recent developments in terms of our relationship with the Soviet Union -- in terms of their support of Operation Desert Shield -- and I think that's. . . the reason that he's not here."

"Any serious analysis of the Soviet military reveals a picture of vigorous internal debates and uncertain intentions, as well as change and instability," Cheney wrote in the review. "What it does not reveal. . . is an eviscerated Soviet force structure and evaporating threat."

The highlights of this year's report included conclusions that:

Soviet defense spending declined about 5 percent in 1989, its sharpest cut in years. But the report notes "even with these reductions, Soviet defense spending is higher than when {President Mikhail} Gorbachev came into power."

The Soviet military is shifting to an emphasis on increasing the quality of new weapon systems and away from its past tradition of producing large quantities of lower-quality equipment.

"Much of what was once certain about the Soviet military is now open to debate. It is not clear how that debate will be resolved."