An easing of Cocom regulations is expected by this summer, but a dismantling of U.S. export controls now is out of the question, said a U.S. assistant secretary of commerce, because the Soviet Union still could pose a threat to the United States.

"Things have changed very fast in Eastern Europe and the Soviet Union, but you can't dismantle overnight the export-control regime," said Thomas Duesterberger, speaking to reporters Sunday at the Leipzig Fair. "It would be a mistake for the United States even to consider totally dismantling it with the evidence that's available to us now."The Commerce official added, however, that the department is "confident that by this summer there will be progress in modernizing" the export-control system. Progress might occur even sooner, he said.

Commerce is committed to reducing the time it takes to get an export license to eight weeks, Mr. Duesterberger said.

Strict U.S. export controls have come in for the most complaints among U.S. exhibitors here, particularly those trying to sell computer equipment to the East bloc. Many say they fear that if the rules aren't changed fast, U.S. companies will lose out in the rapidly developing trade with Eastern Europe.

"I definitely believe that we're shooting ourselves in the foot," said William Tabor, a technical expert at Intraco International Inc., Boca Raton, Fla. Intraco exports U.S. computer equipment all over the world and recently sold East Germany what Mr. Tabor says is the first officially exported Digital Equipment Corp. Microvax II system. Rules permitting the export of the machine were liberalized only a few weeks ago, he said.

"The people over here are not dumb," Mr. Tabor said. "Given the resources, they can duplicate things. Most of the people in the United States would be surprised at where (East Europeans are)."

He noted that the Hungarians already have developed a "counterfeit" Microvax II and East Germany's state-owned Robotron Co. has a Vax 11780, while the Czechs have developed a 11750.

Peter Rasch, director of Rasch Elektronik, a West German firm that serves as a dealer for U.S. computer companies seeking to export to Eastern Europe, said he received an export license for a Sun computer system just two days before the fair opened. Without the license, he said, he would not have attended the fair, because it isn't worth trying to promote a product you can't show to a potential customer.

Mr. Rasch said it is easier to export some computers to China than it is to Eastern Europe, and that's often hard to explain to customers.

"The biggest problem is the regulations," he said, noting that the Taiwanese stand a few steps away from the American exhibit is featuring much more sophisticated computers.

For some sensitive computer items, it can take up to a year to get the needed export license, and this puts U.S. firms at a serious disadvantage, he said.

"In the competition behind the curtain," he observed, "delivery is an important argument to close the deal."