So far, Pat Robertson and Rep. Richard A. Gephardt have emerged as the preeminent demagogues in this political campaign.

Both are beating up on foreigners, an old populist tactic. Robertson, the former TV evangelist running for the Republican nomination, most recently was claiming that the Soviet Union was deploying nuclear missiles in Cuba. The White House denies it. Robertson, however, proceeds to stand by his statement, saying that his only source of information is himself. Later he identified his source as a Senate committee staff member -- who says he doesn't know what's true. The one thing that might have been more irresponsible on Robertson's part would have been if he'd announced that God had told him the Soviets had nuclear missiles in Cuba.

You don't expect these kinds of baseless assertions from presidential candidates, but that is what we're getting. And while Robertson might be dismissed as a fringe candidate, an extremist who is appealing to fear and ignorance, he beat a sitting vice president in Iowa. Somebody out there was listening.

And they were listening to Gephardt, who was also appealing to fear and ignorance on the much more complicated issue of the trade gap. In December, Gephardt, a Democrat from Missouri, wasn't even a household name in Iowa, despite having practically moved there. A poll that month showed he had 6 percent of the vote. Then, on Dec. 26, he began running a series of television commercials that were wrong in fact and in theory. They were a resounding success.

Gephardt took a $10,000 Chrysler K-car and claimed it would cost $48,000 if it were sold in South Korea because of that country's levies on imports. Put in the simplicity that befits a TV commercial: The trade gap with the Pacific Rim countries is their fault, not ours. Gephardt won the Iowa Democratic caucuses with 31 percent of the vote.

It turns out, however, that experts in these matters say the car was more likely to cost about $29,000 in South Korea and that cars made in South Korea are subject to almost all of the same levies as imports.

Gephardt also claimed that an Apple computer that cost $1,500 here cost $3,000 in Japan because of unfair trading practices. According to Alexander D. Van Eyck, president of Apple Computer Japan Inc., the computer costs $3,000 partly because of expenses associated with converting it to Japanese language needs and a decision by Apple to price the computer for a specific market niche.

An article in The Washington Post quoted John Stern, executive director of the U.S. Electronics Industry office in Japan, as saying that a number of American firms doing business in Japan have failed to cut their prices despite the fall of the dollar during the past two years. "It's a calculation of short-term high profits instead of big market share," Stern said. "In fact, most U.S. computer products are much more expensive here. They could charge the U.S. list price and they don't."

His message is quite different from Gephardt's. Stern is saying that many American companies doing business in Japan have made strategic decisions about their pricing and have not made the most out of the falling dollar.

Robert B. Reich, professor of political economy at Harvard's John F. Kennedy School of Government, blew Gephardt's K-car out of the water in an article published in Friday's New York Times. "In the midst of this election year righteousness, it is perhaps useful to consider what 'our' interests really are. Who's 'us' anyway?" he wrote.

"Approximately 30 percent of the total {trade} imbalance is due to American corporations making things {in the Pacific Rim nations} and selling them back to us here, or else buying stuff there and then putting their name on it and selling it back to us," Reich wrote. "And many United States corporations make things there to be sold all around the world." Thus, RCA and AT&T are two of the four largest exporters from Taiwan. IBM Japan is that country's largest computer exporter. The Big Three auto makers imported $5.6 billion worth of auto parts from Asia in 1986, accounting for more than 6 percent of the trade deficit that year.

A lot of the trade imbalance, it would seem, should be labeled "made in the U.S.A." But that's harder to sell than "made in Japan."

This year, economic security promises to be as important a part of the national security debate as military readiness was in 1980. That means it is an all-but-irresistable target for demagogues. They trade on fear, and truth is the first casualty of that kind of campaign. A lot of people, however, are listening.