IN HIS FIRST week as president of Mexico, Miguel de la Madrid Hurtado is off to a strong and sensible start. But his predecessor has left him in an abominably bad position. There is a long and honorable Mexican tradition in which each outgoing president tries to sweep up his own wreckage before the next man arrives. Jos,e Lopez Portillo did just the opposite.

Mr. Lopez Portillo had originally hoped to use Mexico's new oil revenues to catapult the country onto a track of rapid growth and prosperity. But toward the end of his term, the whole strategy began to get badly out of hand, with borrowing running far ahead of earning capacity, and corruption spreading rapidly. Then, instead of rising as the strategy had assumed, the price of oil began to fall. Mr. Lopez Portillo managed to keep things patched more or less together through the presidential election last summer. But in August, after the election, the national economy nearly collapsed. At that point, he began using the long Mexican lame-duck incumbency to embark on a spectacular excursion into left-wing nationalism. The effect is to force Mr. de la Madrid to take responsibility for all of the inevitably unpleasant adjustments ahead.

Immediately upon being inaugurated last week, Mr. de la Madrid began moving in a different direction. He made a series of reassuring appointments, and he introduced a barrage of legislation against corruption. He has begun to raise interest rates, although they remain far behind an inflation that is now around 100 percent a year, and he doubled the price of gasoline to bring it up to the world level. Those are the kinds of changes that are necessary to keep foreign banks lending to Mexico -- which, in turn, is necessary to keep the economy running fast enough to earn its way back toward a rising standard of living.

But there's more to it than satisfying the foreign banks. For Mr. de la Madrid, the hardest part of the passage ahead will be to keep his own country with him through a time of austerity that comes with very little warning after all the expansive promises of the Lopez Portillo years. The new turn has already evoked a hostile reaction from some of the politicians on the left. They haven't counted for much in the past half-century of Mexican politics but, like much else in Mexican politics, that may be changing.

The United States has the strongest kind of interest in supporting Mr. de la Madrid in his struggles to bring his national economy into balance. But beyond that, the United States has a responsibility to do it in ways that will not render life still more harsh for the average Mexican, whose income is perhaps one-sixth that of his American counterpart.