In all of Washington, there may not be two people whose minds work faster than Barney Frank's and Dick Darman's. Frank, the Democratic congressman from Massachusetts, and Darman, the director of the Office of Management and Budget, had an exchange at last week's House Budget Committee hearing that previewed what will be a major -- and useful -- political debate.

In his introduction to President Bush's budget for next year, Darman said the administration was offering "an important new emphasis for reform: increasing fairness in the distribution of benefits, reducing subsidies for those who do not need them."

That passage set off alarm bells among Democrats, who recognize that the "fairness" franchise is one of the pillars of their political power. In the past decade, more and more voters have been telling the pollsters that they think Republicans are better on defense and foreign policy and fighting inflation and promoting economic growth. But just as consistently, those same voters say they think that the GOP is the party of the rich, while Democrats represent the middle class and poor.

Darman's grab for the "fairness" issue went beyond rhetoric. Two of the highlighted proposals in the Bush budget are designed to cut off farm subsidies to people with more than $125,000 in non-farm income and to raise the Medicare premiums for physician and outpatient services paid by people with equally high incomes. Bush also proposed shifting more school-lunch and college-aid funds to people from low-income families.

The immediate changes would be modest -- a few hundred million dollars in a system where individuals receive more than $200 billion a year in government checks. But Darman said he wanted to "start a debate" on the principle of means-testing government programs. And Democrats recognize that is a challenge they cannot ignore -- and might just turn to their advantage.

So when Darman came before the Budget Committee, Frank was waiting. He got Darman to acknowledge that the "losers" in his proposed school-lunch and college-aid reforms would be families with incomes well below the $125,000 cutoff he was proposing for farm and medical benefits. Frank said the break point for school lunches would come when families reached the $21,000 level, and for college aid at about $40,000 -- right at the heart of the middle class.

But Darman was not finished. "I would like to make an offer in very good faith," he said, inviting Frank and other congressional Democrats to find some income level "higher than $20,000 and lower than $125,000" and then "apply it uniformly across the board" as the cutoff point for "a whole range of mandatory {benefit} programs apart from Social Security."

"I think it is absolutely sound on the merits to have some general means-testing principle, except with respect to Social Security," he said, "and I believe genuinely that the political system will be forced in that direction . . . over the next decade."

Darman is far from the first to make that judgment. In the 1988 Democratic presidential primaries, former Arizona governor Bruce Babbitt (D) argued for means-testing entitlement programs. In an era of scarce governmental resources and unrelenting demands for public services, he said, subsidies for the rich have no justification.

But there's a problem for Democrats, as Rep. Jim Cooper (D-Tenn.) reflected at the hearing. "By all of a sudden taking Medicare and making it a welfare program," he told Darman, "or taking farm programs and making them a welfare program, you would be undercutting the national consensus that has built and preserved these programs. . . . With your ingenuity, you may well be launching a very powerful concept to stigmatize the beneficiaries of big government. . . ."

Darman angrily rejected that suggestion, but Cooper's concern has strong historical roots. Over the years they controlled government, Democrats built political support for their spending programs by targeting them broadly -- not narrowly -- and giving millions of middle-class voters reasons to support programs that were helpful to them, but vital to the poor.

In a time of chronic deficits, few Democrats believe that policy can continue. But to win the debate, they need to broaden the definition of "fairness," as Senate Majority Leader George Mitchell (D-Maine) did last week.

Mitchell released a Senate Democratic agenda that points out that a decade of Republican economic policies have made this a nation "in which the richest 20 percent of all Americans earn more than all the rest of our people combined." He pledged to push for policies that will "lessen the tax burden on working families" while asking the wealthy "to bear a greater share" of the bills.

Framed that way, the fairness debate Darman wants is not one the Democrats need fear. And more important, it's one from which the country can benefit.