In 1978, Ronald Reagan told a joke about an employee who asks his boss to cut his salary and thus make him eligible for a public housing project -- ''the one downtown with a pool, sauna and tennis court.'' The boss agrees, then asks to be invited over for tennis. ''Certainly, Sir,'' the employee says. ''I believe the poor should share with the less fortunate.''

The story was one of many in the future president's repertoire of welfare jokes, which he told with much effect. Truth was beside the point. He sensed -- and he himself felt -- the widespread rage at welfare abuse. Much of the nation felt ripped off.

The latter-day Ronald Reagan is Richard Gephardt. His issue is not welfare, but trade. Clearly, he has learned something from the president. He senses -- and he himself might really feel -- the growing frustration of Americans as they see their country slip from economic king of the mountain to something markedly less.

For instance, Bridgestone, a Japanese firm, just bought most of Firestone's tire operations. Firestone has long been synonymous with tires and American dominance of the industry. It had plants worldwide and rubber plantations in foreign countries. Now the company is substantially out of the tire business.

When it came to welfare jokes, Reagan had the help of countless straight men. They were Democrats, particularly liberals, who refused against the weight of all the evidence to concede something was wrong with the welfare system. With evidence accumulating of cheating and the inability of the welfare program to raise some people out of poverty, liberals nevertheless defended their creation. They seemed to feel that to concede imperfections was to concede the totality of the conservative argument: all of welfare was an expensive and immoral joke.

It's the same with trade. Gephardt is on to something. Trade restrictions do exist. We have them and so do our trading partners. Sometimes, they work to our disadvantage and something ought to be done about them. Yet much of the ''establishment'' is so enamored of ''free trade'' that it will not concede that such a thing does not exist. What it fears most is a popular demand to protect American jobs by erecting trade barriers -- possibly triggering a worldwide economic depression.

This Reagan-like ability to distill and package a message, to strike a chord in the American people, is to Gephardt's credit. The trade message he now espouses is approximately the same one he espoused a year ago. Back then, however, he also pointed out that the bulk -- maybe 80 percent -- of America's trade problems was internal. In some markets, trade restrictions play almost no role at all. American industry simply cannot compete. But now, the imperatives of the 15- and 30-second spot have been imposed. On television, a sophisticated analysis has been reduced to a simplistic call for retaliation. It has worked for Gephardt, but it won't work for the economy.

Most comparisons eventually run out of steam, and comparing Reagan on welfare with Gephardt on trade is no exception. By 1978, Reagan had spent 14 years championing conservative principles. He was a known commodity. That's not the case with Gephardt -- an alleged political chameleon who takes on the coloration of the constituency he's wooing at the moment. If his opponents were to make a 15-second campaign bio of Gephardt, the Righteous Richard of old would metamorphose into Demagogue Dick. His opponents are furious with him.

But politicians should heed the message and not just attempt to rebut the messenger. Gephardt has a point about trade barriers, and he's saying something about America that's as obvious as a parking lot full of Hondas: the erosion of American power and prestige has yet to be dealt with, and many people feel they are being ripped off and played the patsy by foreign governments.

When Reagan's gibes at welfare mined feelings of frustration, they were dismissed as simplistic. Almost everyone said so. Only the voters disagreed.