By a fortuitous circumstance for the Democrats control of the Joint Economic Committee of Congress -- chaired this past session by Democratic Sen. Lloyd Bentsen of Texas -- will stay out of Republican reach for the next two years, despite the sweeping GOP victories in the Senate.

As it happens, chairmanship of the Joint Economic Committee rotates between the Senate and the house -- still Democratic -- and it becomes the House's turn next year. And in that circumstance, Rep. Henry S. Reuss (D-Wis.), who will be serving his final terms, has exercised his option to take over the JEC chairmanship, yielding up the House Banking Committee.

It was an interesting choice for Reuss to make, and promises not only a searching, "keep 'em honest" look at Reganomics but, if Reuss maintains a tentative agenda he's set for himself, a retrospective look at the Democratic failures of the past four years.

A bit wan, but on the road to recovery from heart bypass surgery, Reuss told me that he's not proposing a witch hunt or "a retrospective chamber of horrors." He put it this way: "Economics are the leading domestic problem, from which most of our others stem. We Democrats didn't solve the problem, and it's the main reason why we were heaved out."

Some Capitol Hill veterans were surprised that Reuss would give up the baton at the powerful banking committee, one of the key legislating units on the Hill, for the non-legislating JEC, which in recent years has lost some clout. With the creation of a budget committee in each house, and acquisition by the banking committees of new surveillance power over Federal Reserve monetary targets the JEC's influence has been diluted.

"But that's really not a loss, the way I see it," Reuss said. Macroeconomic fiscal and monetary policy aside, he argues, what is really important are four or five key "microeconomic" areas where he feels national policy may have gone astray. And these he proposes dto deal with in detail at the JEC over the next two years.

For example, the JEC will take a look at the many proposals for "reindustrialization" of the economy. "Obviously," Reuss said, "bailing out the losers, as Carter did, is not a good way." Picking winners would be fine, but Reuss confesses that "how you pick them" remains a mystery. He seems disposed to reject a new government Reconstruction Finance Corp., and to concentrate instead on removing disincentives such as those he says block regeneration of rail and mass transit systems.

In seeking answers to the seemingly intractable problem of stagflation, Reuss rejects wage-price controls. But he says that the JEC will study whether it is possible to have a "social contract" between labor and management along West German lines. He acknowledges that the incoming Reagan administration is completely opposed to any form of wage-price intervention, but needles: "So was the Nixon administration!" (which actually imposed a wage-price freeze in 1971).

Another area that Reuss is staking out for the JEC is what he calls "the income distribution effect of Reaganomics." He assumes that a good part of the Reagan tax-cutting and budget-cutting demands will get through Congress, "shifting income away from the bottom 60 percent toward the top 10 or 20 percent." The Jec spotlight will be kept on such Republican proposals as reduced capital-gains taxes and tax credits for private-school tuition.

In addition, Reuss feels that the shift from health, education and other "people-oriented" budget programs to the military will exacerbate existing regional disparities, notably the growth of the Sun Belt states at the expense of the Midwest. A total focus on "supply-side" economics could wind up with insufficient demand, leading to deep recession, or even "civil commotion," the Wisconsin congressman believes.

One of the touchiest areas of inquiry that Reuss has plotted out is whether or not some existing tax incentives have had a perverse effect. For example, he argues that $20 billion in interest deductions for housing mortgages feed middle- and upper-bracket purchases of luxury homes -- often energy inefficient. He also bravely suggests that subsidized loans (7 percent) for well-to-do college kids may have something to do with the weaknesses of America's volunteer army.

Reuss may have a tiger by the tail in tackling these "wrongheaded incentives," especially mortgage-interest deductions. And the 20-member JEC, split down the middle between Republicans and Democrats, won't support all of Reuss' probes and sallies into the unknown world of Reaganomics. Nonetheless, there is a prospect that given Reuss' enthusiasm for the assignment, the truncated JEC over the coming months may provide a lively economic watchdog role for Congress and public.