US gross domestic product may be reduced only by one-half of 1 percent at worst as a result of a Japanese crisis, said Brian Levitt, economist at Oppenheimer Funds.

According to Levitt’s view, exports account for only 10 percent of U.S. GDP, and Japan accounts for only 5 percent of that number. "Five percent of U.S. exports—10 percent of the U.S. economy—so one-half of one percent to U.S. GDP at the absolute worst," he told CNBC Wednesday.

"It's a little too soon to put an absolute hit to GDP on all of this," he added. "For those of us sounding an optimistic bullish call heading into 2011...we do have to curb our enthusiasm a little."

At the imports side, Japan accounts for 6% of U.S. imports, most of them from the automobile and parts sector, he said. Supply disruptions remain to be seen, he said, though U.S. suppliers may get around any interrupted components from Japan with their own products.