A top State Department official said yesterday that the time hasn't come "to pronounce the death of detente" with the Soviet Union.

But the United States doesn't intend to set any time limit for the withdrawal of economic sanctions against the Soviet Union, Deputy Secretary of State Warren M. Christopher said.

The sanctions, mainly the denial of 17 million metric tons of U.S. grain ordered by the Soviets, will remain in place for a "considerable duration," he said on "Face the Nation (CBS-TV, WDVM).

"I don't expect to go back to business as usual with the Soviet Union for some time to come," he said.

Christopher was questioned mainly about the Soviet intervention in Afghanistan, his recent trip to Europe to consult with U.S. allies in the North Atlantic Treaty Organization and the current trip of Defense Secretary Harold Brown to China.

In connection with Brown's trip Chriistopher twice declined to rule out the possiblity that American radar stations for monitoring the Soviets may be established in China. Such facilities would make up for the loss of radar stations in Iran.

The first time he was asked about the facilities, Christopher reiterated the U.S. policy of not becoming an arms supplier to China. The second time, he said, "I really wouldn't have any comments, except to say that we will be discussing [China's] possible aid to other countries in the region that might be threatened by the Soviet behavior."

As to Afghanistan, Christopher said that the Carter administration is determined to show the Soviets that their intervention carries "considerable cost to them" and that similar aggression hereafter will bring "very severe penalties.

In this connection, he recalled the Soviet invasion of Czechoslovakia in 1968. The administration believes that the Johnson administration made a mistake in not taking long-term punitive action against the Soviet Union. "One of the lessons coming out of the Czecholovak crisis is that the response needs to be determined and of considerable duration," he said.

He also said the Carter administration "expects" two leading wheat-producing countries, Canada and Australia, and the NATO nations to take actions that parallel and support American economic sanctions. He did not mention Argentina, another leading wheat producer.

Christopher said he believes the NATO allies decry the Soviet intervention as much as the United States does and will be "determined and firm."

Asked if he knows why the Soviets sudenly sent their armed forces into Afghanistan, Christopher said, I don't think anybody knows . . . ." He said the intervention could be "a stepping stone" toward "a broader interest," such as access to a warm-water port or additional sources of oil. Oil-rich Iran borders on Afghanistan as well as on the Soviet Union.