The nation, and especially the Democratic Party, is learning that it better take the Rev. Jesse Jackson seriously. Jackson did better in Iowa, New Hampshire, Minnesota and Vermont -- states in which there are few black votes -- than any of the so-called experts had predicted.

On the televised debates, he plays the role of the moderate peacemaker, competent and thoughtful, worrying about the consequences for the "team," as Dukakis, Gore and Gephardt snipe at one another. It's a smooth performance, and obviously more productive than the "Rainbow Coalition" campaign of 1984. But some make an assumption that as a black man, Jackson can't make it to the presidency -- or to the vice presidency. So why pay attention to what he's saying?

That's a mistake: Jesse Jackson is a dynamic and compelling force, and should be taken seriously. As he shrewdly observed on the "McNeil-Lehrer Newshour" the other night: "There's a tendency to keep underestimating the impact of our work. They never thought we would have double digits in Iowa, that we would beat Simon in Minnesota. We keep defying these odds, we keep taking our case directly to the people. I must tell you that people are responding."

Jackson, like the other candidates, should be examined in terms of what he says he stands for. And what Jackson is selling is a powerful and dangerously seductive brand of economic populism and economic nationalism.

Although much of Jackson's analysis of the country's problems is not dissimilar from that of his fellow Democratic candidates (with good reason, they place much blame on Reaganomics), his solutions drift to the left of the liberal wing. Who else among the other five would demand "a code of conduct for American business, to ensure that its investment decisions are made in the best interests of the community"? Measure that one in terms of a potential drop in the Dow Jones index!

Jackson's corporation-bashing also calls for higher taxes on business to pay for his numerous education, training and social welfare initiatives.

He has worked hard to avoid a Gephardt-like label as a protectionist. Yet, like Gephardt, he cites automation as the villain causing a "shift from the relatively well-paying union jobs in manufacturing to unorganized poverty jobs in the service sector; these are profound tendencies which strike at the middle class as well as the poor, at whites as well as people of color."

The difference is that where Gephardt has made a fetish of the unfair trade practices of Asians and Europeans, Jackson focuses on corporations exporting American jobs and capital. "Our jobs are not being taken by South Koreans and Taiwanese," he tells his audiences. "They are being taken to South Korea and Taiwan by U.S. companies with tax incentives."

He calls for "an international affirmative-action plan to protect organized American workers from unfair competition of unorganized foreign workers." The diagnosis, aimed at companies such as General Electric, hits the target. But we are left to wonder how that "international affirmative-action plan" would work. A Jackson aide tells me the candidate aims to have labor practices that are considered unfair by international authorities deemed unfair trade practices open to retaliation by the United States.

Last Saturday, during the Democratic debate in Atlanta, Jackson warned -- without backing it up -- that "foreign investment is buying critical industries like banks and communications." That fans the current hysteria over charges that Japan is "buying up" America at a discount, even though Japan owns only a small, if growing, percentage of American assets.

To stimulate growth at home, Jackson calls for a huge public works effort, perhaps $6 billion a year over a 10-year period. Labeled "Invest America," this plan would tap private pension funds for the money to rebuild America's roads, bridges, sewerage treatment facilities and harbors.

Clearly, this would be a risky adventure threatening the security of pension funds. So Jackson wants federal guarantees for it, the potential cost of which to the taxpayer is hard to calculate.

But despite this menu of bold, untested and maybe wild and woolly ideas, Jackson's following seems to be growing. Who can fault his stirring attack on the administration's failure to deal with the insidious drug traffic? And like his fellow Democratic candidates, he has slipped into the increasingly popular but isolationist posture of advocating sharp reductions in American financial support for troops abroad (ignoring huge foreign manpower commitments, especially in Europe, to global security).

Before it's all over Jackson will accumulate a highly respectable clutch of votes and delegates, and will be a major factor in shaping and influencing a left-looking, isolationist Democratic Party agenda.