DES MOINES, JULY 20 -- Reps. Jack Kemp (R-N.Y.) and Richard A. Gephardt (D-Mo.) faced off in a debate on U.S. trade policy today, with Kemp accusing Gephardt of proposing protectionist legislation that would lead to a ruinous trade war and Gephardt countering that the policies of Kemp and the Republicans have made the United States a world "trade patsy."

In a spirited but generally good-natured one-hour debate at Drake University, Kemp charged that Gephardt's proposed legislation, aimed at forcing Japan and other major trading partners to open their markets to U.S. products, would lead to retaliations in kind that would result in "mutually assured economic destruction."

Gephardt retorted that Japan hopes to sell $20 billion worth of automobiles in this country this year while South Korea hopes to sell 1 million Hyundais.

"But we are precluded from selling our beef or Louisiana rice or pork or processed goods to them," he said. "Their tariff on our chicken is 65 percent, our corn and pork exports are down 65 percent and soybeans are down 30 percent. Does anyone really believe that Japan would close its markets to our farm products more than they already are and risk the sale of $20 billion in automobiles?"

The debate, carried on cable television, was the second this year between two presidential candidates of the opposing parties, and others are under discussion. Kemp and Gephardt previously debated each other in 1985 and 1986.

Kemp complained that Gephardt's get-tough policy was aimed at this nation's major trading partners and likened it to the Smoot-Hawley tariff of the 1920s and 1930s, an across-the-board trading wall on all imports. Kemp, playing a bit loose with history, blamed the Great Depression and the Democrats' emergence as the majority party on Smoot-Hawley.

"Now in an ironic reversal, the Republicans are the party of free trade and the Democrats are the party of protectionism," he said. "Their solution to everything is to raise taxes and tariffs. Mr. Gephardt said recently that under Ronald Reagan it's now darker than midnight. That's typical Democratic doom and gloom."

Gephardt's proposal would just invite retaliation, he said. "The very first act of the Europeans would be to enact mirror legislation," he said.

The other Democratic candidates have been critical of Gephardt's legislation, labeling it protectionism and anti-free trade, as Kemp does, and warning of retaliation.

Gephardt argued that he is "finally proud of Reagan" for making the Japanese back down on dumping semiconductors in this country. "They'll do that when they realize that we really mean business," he said.

Kemp, however, scoffed at this.

"I thought that semiconductor deal was an outrage," he said. "It just made PCs {personal computers} more expensive because the cost of the chips has gone up from 75 cents to $1.50."

Both agreed that economic growth and more productivity are needed to improve America's competitive position in the world.

"We need to educate our kids, be able to defend ourselves and pay our bills, but the Reagan administration has steadily cut aid to education," Gephardt said. "The policies of the last seven years have not made us stronger and more competitive. We're getting weaker every year."

Kemp proposed an international economic summit aimed at lowering trade barriers. "What we need is an honest, stable dollar, lower interest rates and less impediments to the productivity of our workers, farmers and businessmen," he said. He has proposed pegging the value of the dollar to gold and other commodities as a means of keeping it stable and protecting it from fluctuations in world money markets.

Gephardt scoffed at this. "I'm not in favor of being in a position of having the Russians and the South Africans telling us what our dollar is worth."