If cropland and livestock contamination from the Chernobyl nuclear accident force the Soviet Union to buy more food abroad, the surplus-burdened United States is the last place Moscow is likely to look, a congressional committee was told yesterday.

Dwayne O. Andreas, the top official of one of the country's largest grain handling firms, and several commodities analysts said that continuing American high prices and unfavorable trading terms probably will send the Soviets elsewhere to augment food production.

Their assessment -- if correct -- could quickly dash speculation in the American agriculture sector that last week's Soviet nuclear disaster could create a heavy demand for U.S. farm goods and reverse a downward trend in prices.

One of the analysts, John M. Urbanchuk of Wharton Econometric Forecasting Associates, said that on the basis of limited knowledge of radioactive damage in the Ukraine and neighboring Soviet republics, he would assume no more than a 10 percent crop loss -- akin to one of the Soviets' frequent bad-weather years.

"This outcome would be about the size of the 1984 Soviet crop and would be the third smallest in 12 years," Urbanchuk said in testimony before a subcommittee of the Joint Economic Committee of Congress.

"The Soviets may find it necessary to increase imports of grain, dairy products and possibly meat," he said. "In the case of increased dairy and meat imports, the most likely beneficiaries will be the European Community and possibly East Europe, notably Poland and Hungary. The Soviets will likely continue to increase wheat imports from non-U.S. sources, but rely on the United States for additional coarse grains."

Andreas, head of the Archer-Daniels-Midland Co. in Decatur, Ill., agreed, saying that the United States might end up selling some corn and some soybean meal, but that high prices on other commodities would send Soviet shoppers to other markets.

"It is unlikely that U.S. farmers would benefit from any additional wheat purchases," he said, since wheat is cheaper in France, Argentina, Australia and Canada -- all major producers. "We cannot expect them to buy soybean oil here . . . it is likely they would come here for corn," he said.

Both he and Urbanchuk also noted that the new American export enhancement program, which subsidizes overseas grain sales, could not be expected to meet the competition because of a Reagan administration decision to deny subsdized sales to the Soviet Union and other communist countries.

Another analyst, Donald Frahm of Sparks Commodities, said the instant reaction in American futures markets that sent wheat and corn prices soaring last week was predictable, but that the Chernobyl incident "is likely to go down in history as an insignificant event for U.S. commodity markets."

Sen. James Abdnor (R-S.D.), vice chairman of the committee, added another discouraging footnote to forecasts that U.S. farmers' fortunes would not improve as a result of the nuclear station accident.

"Remarkably, some commodity prices may well settle lower than levels prior to Chernobyl. Futures markets continue to bewilder me, and nine out of 10 farmers and ranchers, I might add," said Abdnor, a farmer-rancher in private life.