Mexico wins fiscal reprieve, but for how long?

Mexico has won a brief breathing space to put its economic house in order.

But time is short.

Unless the multibillion dollar bailout package announced over the weekend in New York and Washington is accompanied by a thorough-going and immediate economic housecleaning at home, the specter of national bankruptcy which loomed so large in recent weeks could return ''with a vengeance.''

That estimate by one of Mexico's leading bankers this weekend reflects the deep lack of confidence in the lameduck Lopez Portillo administration evident just about everywhere in Mexico.

But Mexico's problems are much more than a mere lack of confidence in the government.

There simply isn't any money in the till to pay the whopping $80 billion foreign debt, much of it contracted in the past five or six years. For a nation that put so much emphasis on its newfound oil wealth in these years, this is an extremely humiliating position. It wasn't suppose to happen this way. That oil wealth was supposed to pay for everything - all the massive development schemes aimed at improving the lot of the average Mexican.

Now Mexico finds itself in the position of begging for a bailout with its sombrero in hand and it has turned to Finance Minister Jesus Silva Herzog to carry out the task.

For the past two weeks, he shuttled back and forth between Mexico City and New York and Washington in determined efforts to avoid immediate default on his country's massive foreign debt.

The efforts have been successful, but the success is at best only temporary.

Still at week's end, Mr. Silva Herzog had won agreement from the United States government and US private bankers, from foreign bankers, and from other international lenders on a multibillion dollar bailout package that will give Mexico some much-needed, albeit temporary breathing space.

The package includes:

* An advance $1 billion payment by the US government for Mexican crude oil destined for the US strategic petroleum reserve, which serves as a protection against future disruptions of foreign supplies. Further increases of US purchases of Mexican crude are possible in the months ahead.

* $1 billion of guarantees by the US on new loans by US commercial banks, many of which have loaned Mexico billions of dollars. The loans also could be made available by midweek.

* $1.5 billion in new loans from foreign central banks. This money will become available at midweek.

* A rollover of three to six months on $10 billion in foreign debts due now. Mexico must pay interest payments on these loans as they come due and can use some of the money from the new US and other foreign bank loans to make the payments.

In addition, up to $4.5 billion in credits from the International Monetary Fund (IMF) will likely be made available to Mexico by mid-October. Talks between Mexican officials, including Mr. Silva Herzog, and the IMF have been going on for several weeks - and an IMF team is now in Mexico City.

But the Mexican government, to receive these IMF credits, will have to agree to a number of austerity measures including a freeze on wage increases, a lid on prices, and deep budget cuts. Such moves will not sit well with Mexico's restless labor movement nor with hard pressed businessmen.

Moreover, even with the bailout help negotiated by Mr. Silva Herzog this past week, there is no assurance that Mexico can find the money to pay the foreign debts coming due later this year. The heavy debt burden simply may be too high for the Mexican economy to absorb.

The situation is further complicated by the presidential transition due Dec. 1 when President Jose Lopez Portillo turns the sash of office over to Miguel de la Madrid Hurtado. This fuels uncertainty about the future. Mr. Silva Herzog is obviously the key individual at the moment. But his tenure is likely to end Dec. 1.