For the past four years, Ronald Reagan has preempted the economic issue, first with the "supply-side" mystique that was so new that even some dubious critics urged it be given a chance.

Then, although a budget balance proved to be a mirage, fancy depreciation allowances and other tax cuts gave the economy enough of a Keynesian stimulus to touch off a recovery that silenced Democratic tongues during last year's election.

In effect, the Democrats have had no economic agenda, beyond a mistaken faith in protectionist measures for old-line industries linked to old-line unions. Only recently, as the Reagan administration began its push for budget cuts that would further slash social programs, have some Democrats come alive to the need to generate alternative ideas.

There still is no cohesive overall Democratic program. The Democrats on the Joint Economic Committee have just released some general recommendations to reverse the mix of fiscal and monetary policy. Yet they shy away from a tax-increase proposal with all the fervor of Ronald Reagan.

Still, some bits and pieces are coming together, suggesting that not all Democrats have forgotten how to think. Gary Hart (D-Colo.), for one, has just introduced a package of bills elaborating on some of the ideas he had floated for investment "in the human mind" in his unsuccessful -- but close -- campaign to wrest the 1984 nomination from Walter Mondale.

Last session, Rep. Pete Stark (D-Calif.) proposed that unemployed workers be allowed to take unemployment compensation benefits in a lump sum for retraining or relocation.

Now Democratic Reps. Ron Wyden of Oregon, Richard Gephardt of Missouri and Charles Schumer of New York offer a tantalizing variation of the Pete Stark proposal: Let a small number of unemployed workers take six months' unemployment benefits in a lump sum for the purpose of starting their own businesses. Under current federal law, an unemployed worker cannot attempt to become self- employed and still receive benefits. Hart is introducing a Senate version of the Wyden-Gephardt-Schumer bill.

Former Jimmy Carter aide Stuart Eizenstat thinks these proposals have merit and makes the key point: "We Democrats have to counter the idea that all we're interested in is welfare and income maintenance. We have to come up with more creative thinking."

As explained by Wyden, the "Self-Employment Opportunity Act of 1985" will help some unemployed persons take control of their own future -- and employ others along the way. Wyden-Gephardt-Schumer would empower the secretary of labor to test out the lump-sum payment program in five to 10 states, with no more than 5 percent of those getting unemployment compensation in a given state eligible to participate.

Their plan is modeled after similar successful experiments in France and England since 1979, and copied in other European nations.

It's clear that the start-your-own-small-business notion won't mop up more than a tiny fraction of the 8 million on the jobless rolls who may have neither the additional resources, talent nor inspiration to generate a new enterprise. "But we're convinced that there are thousands of people in the unemployment lines today -- from all walks of life and with all sorts of qualifications -- who are capable of becoming self-employed," Wyden said.

He cites as a theoretical example an unemployed plywood mill worker in the Portland area who cannot find new job opportunities using his particular skill. He might take his $204 weekly compensation for 26 weeks and keep looking for a job.

Or, if he's got guts and an entrepreneurial drive to go along with his skills, he could, under the Wyden-Gephardt-Schumer proposal, take a lump sum of $5,304 to start a business (say, selling and repairing chain saws) if the state labor department gives the project an okay.

To be sure, $5,304 isn't a lot of money (26 weeks' worth of unemployment compensation would be barely over $3,000, on the average, in most other places in the United States). Milwaukee Journal reporter Jim Rowen, who has studied alternative state-local support programs, suggests allowing several unemployed workers to bunch their lump sums to finance new business operations -- a twist the Wyden staff thinks has merit.

The conversion of unemployment compensation into investment money could turn out to be a pipe dream. But there is something appealing, and in the American spirit, about the prospect of giving an individual down on his luck a shot at making it on his own.

So Hart, Stark, Wyden, Gephardt and Schumer are to be commended for being willing to sponsor legislative experiments. But more and broader-scale aternatives to the presen economic drift are necessary before it can be said that the Democrats have a respectable economic agenda with which to contest Reaganomics. The Humphrey-Hawkins Act requires the president, Congress and the Federal Reserve System to aim at full employment. The current 7-plus percent unemployment level certainly doesn't qualify.