THERE WAS a discordant moment in President Bush's address to Congress last week that reveals the new political terrain of the 1990s.

After Bush described the mission behind Operation Desert Shield in expansive terms -- nothing less than the defense of "civilized values" and the creation of "a new world order" -- he turned soberly to domestic affairs. The American people are "sick and tired" of the federal budget deficit impasse, he warned Congress. "It's high time we pulled together and got the job done right."

Was our commander-in-chief about to summon us to make sacrifices? To have us ask what we could do for our country? Not exactly. What he had in mind was a tax cut.

In fact, he proposed a satchelful of them -- expanded IRAs for new homeowners, tax incentives for oil drillers, tax-deferred savings plans and -- the big one that got the loudest cheer from the Republican side of the chamber -- a capital-gains tax cut.

A few minutes later, House Majority Leader Richard Gephardt (D-Mo.) gave the televised Democratic response. "Just as we must ask wealthy nations to pay their fair share to deter agression," he said, "so must we ask wealthy Americans to pay their fair share to prevent recession and reduce our debts."

A new line was drawn in the sand that night -- or, more accurately, an old line reappeared after a decade-long absence from domestic political debate: Democrats who want to soak the wealthy vs. Republicans who want to coddle them.

Gephardt's speech marks the formal end of a decade of Democratic acquiesence in favor-the-rich, trickle-down economics. Remember: It was Republican ideology that drove the top marginal income tax rates for the wealthy down from 70 to 28 percent, but it was also Democratic votes.

Those top-rate reductions, combined with a steep decade-long rise in the Social Security tax, have made the federal tax system considerably less progressive today than it was a decade ago. According to a Congressional Budget Office study, the poorest quintile (20 percent) of American families are paying 16.1 percent more of their family income in federal taxes today than they did in 1980, while the richest quintile are paying 5.5 percent less -- and the super-rich, the top 1 percent of families, are paying 14.4 percent less.

This shift has ended the doctrinal warfare within the Democrat Party on tax matters. Virtually everyone in the party is now aboard the progressivity bandwagon. Gephardt, Democratic National Committee Chairman Ron Brown and New York Gov. Mario Cuomo all said so in various forums last week. Even the Progressive Policy Institute, a think tank established by the party's business-oriented, moderate-to-conservative wing, has called for making the Social Security tax more progressive by eliminating the cap and lowering the rate. Indeed, tax equity between rich and poor was the key sticking point among congressional and administration leaders who holed up last week at Andrews Air Force Base to hammer out a budget deficit reduction plan.

With the budget negotiations in full swing, Bush might have used the Persian Gulf crisis, and his attendant spike in popularity, to defuse the gathering force of the progressivity issue by pointing to the new burden and calling for sacrifice from those most able to shoulder it. Instead, he chose to make one last run at a supply-side capital gains tax cut -- more than 80 percent of the benefits from which would accrue to Americans who earn $100,000 or more.

Republicans have reaped a decade of electoral blessings for being the party of tax-cutters. But as the agenda has shifted from cutting taxes to cutting deficits, the terrain has gotten more difficult. Two months ago, Bush's retreat on his 1988 "no new taxes" pledge threw the GOP into a state of tax policy confusion.

Most Republican candidates this fall continue to oppose all new taxes. But some, notably the GOP nominees in two of the nation's most crucial gubernatorial races -- Sen. Pete Wilson of California and Secretary of State Jim Edgar of Illinois -- are supporting increased taxes: Wilson to fight drugs; Edgar for education. The pair may represent the beginnings of a 1990s revival of moderate Republicanism.

But Bush, having been burned once, blurred matters last Tuesday by talking about tax cuts -- even as his budget negotiators were busily horse-trading with the Democrats over which taxes should be raised.

Whatever the outcome of the budget talks, there is a bipartisan consensus on the need for a five-year, $500 billion deficit reduction plan, and it will eventually force some tax increases to be enacted, quite possibly this fall. At that point, the issues of who pays what -- and of who enjoyed the tax party in the 1980s and who didn't -- will be squarely on the table.

These questions are more likely to ripen, politically, in 1992 than in 1990. It's been a long time since there's been a full-fledged equity debate in this country, and it will take a presidential campaign to do it justice. How all this plays with the voters will depend less on the state of their consciences than on the state of their pocketbooks. If middle-class Americans are hurting, they may well be in a mood to punish the rich. If they aren't, they won't be. They'll be too busy expecting to be rich themselves.

There are two larger points about 1992 that Tuesday night's speeches have already made clear. One is that the new partisan battle for the middle class will be waged on economic rather than on cultural grounds. That's good for the Democrats, because most cultural issues -- race, crime, morality, patriotism -- are political losers for them.

The other is that the president has lashed his political fortunes to Operation Desert Shield. In the short term, this has had only political benefits. But the long-term picture may be dicier. As Democratic strategist Ted Van Dyk notes, "The trouble with raising the stake {in the Gulf} so high is that anything short of kicking Iraq out of Kuwait will be seen as a failure . . . . The trouble with keeping troops over there for the long haul is that it's hard to sustain public support for wars that aren't clear-cut."

Crisis management and foreign policy have given Bush's presidency definition. Even if the crisis doesn't end exactly the way he would like, he may be grateful to have a story to tell in 1992. Right now, the domestic saga doesn't look like it's going to worth bragging about.

Paul Taylor covers politics for the Washington Post.