"The problem is that we've got a president that campaigns like Superman and lobbies like Clark Kent."

I wish I'd said that, or could tell you who did. (It was an unidentified congressional aide quoted in The New York Times.) But never mind the authorship; it's the metaphor that matters. Taken in a general way (for "campaigns" read "looks"; for "lobbies" read "performs") it serves wonderfully well. It explains not just the president's handling of the tax reform crisis in the House, to which it was addressed, but the particular nature of the Reagan presidency over most of the past five years.

What we see is Superman jumping over the heads of Congress to the American people -- soaring up, up in the public approval ratings measured by the polls. Look at him up there promising a balanced budget, no tax increases, superior defense, an astrodome against nuclear war, freedom for freedom fighters and all other good things befitting Superman.

But what we get is Clark Kent. When push comes to shove, at home or abroad, we get this decent, earnest fellow, fumbling in his grasp of the essentials of his Strategic Defense Initiative, or of arms control, or of other important foreign policies; incapable of maintaining order in his own administration; embattled against congressional encroachments on his presidential power and prerogatives.

It was Ronald Reagan/Clark Kent who had to go hat in hand at the last minute to a caucus of his own party on Capitol Hill in search of Republican support for an essentially Democratic version of the first big domestic order of business in his second term. His turning around of enough Republicans to get the tax reform bill through the House could be seen as evidence of thresident's powers of recovery.

But that still doesn't explain the extraordinary exertions required by the president to rescue from the hands of his own party a program for which he has been stumping the nation for much of this year while reaching new heights in public approval polls. It is this disconnect between extraordinary popularity and the effective exercise of power that makes the tax reform voting less of a turning point than a commentary on the Reagan phenomenon.

Try to imagine another president in recent times who could stand so high in the ratings with only the battle of Grenada to prove his mettle as a relentless resister of communist expansion. Think of one who could stand tall while walking away from Lebanon after vowing to stay there for as long as it took to safeguard Middle East peace and global security; who could promise "swift retribution" against terrorists and then do nothing.

Granting the early successes in revising spending priorities, diminishing government activity and launching a popular defense buildup, you are still left with a record that few presidents could turn into either a sweeping reelection triumph or top ratings in approval polls. By way of examples we have the botches of the mining of Nicaraguan harbors, of the ceremonies at Bitburg, of the European natural-gas pipeline.

The Reagan Middle East peace initiative goes nowhere. His equally celebrated "Star Wars" initiative confounds policy making on arms control. No better than half-a-loaf from Congress has been the role on aiding Nicaraguan "contras" and the MX missile. He has caught himself up in the fiscal winding sheets of Gramm-Rudman's deficit controls.

And now come the tax reform travails to compound the puzzlement of even his own party stalwarts. "It's odd," says Republican Sen. Charles Grassley of Iowa. He thinks the president is too popular to be in a "lame-duck position." Like other Republicans, he blames White House attitudes. "When they wanted us, they called. When we wanted them, they were generally too busy." He has a point: archconservative ideologues, with which this administration is richly endowed, are not good listeners and still less inclined to wheel and deal.

But I like the Superman/Clark Kent explanation the best. Superman is for hard- core conservative spectators. The real Reagan is Clark Kent, a closet pragmatist.

The act may not work indefinitely. As time runs out on the second term, Ronald Reagan/Clark Kent may become less and less able to work the magic of Ronald Reagan/Superman. But whatever you may think of the results, when you look at the record, you have to marvel at the way he has been able to work it for so long.