By GINGER THOMPSON

MEXICO CITY, March 8 — President Miguel de la Madrid governed Mexico for most of the 1980's, through one of its most painful economic crises, a devastating earthquake and a period of diplomatic tensions with the United States. But perhaps the most widely scrutinized act of his presidency came on the night in 1988 that his successor, Carlos Salinas de Gortari, was elected.

In an autobiography that began circulating in Mexico this week, Mr. de la Madrid sheds more light on that dark night in Mexico's history. What he reveals is not new, political analysts said. But in 850 pages, Mr. de la Madrid's memoirs give the firmest confirmation to date of one of this country's biggest open secrets: the presidential elections of 1988 were rigged.

Political analysts and historians have described that election as one of the most egregious examples of the fraud that allowed the Institutional Revolutionary Party to control this country for more than seven decades, and the beginning of the end of its authoritarian rule.

Initial results from areas around the capital showed that Mr. Salinas was losing badly to the opposition leader Cuauhtémoc Cárdenas. "I felt like a bucket of ice water had fallen on me," Mr. de la Madrid recalled. "I became afraid that the results were similar across the country and that the PRI would lose the presidency."

Thus began the frantic staging of a fraudulent victory. In his writing of the event, the all-powerful former president chooses his words carefully and describes himself more like a supporting actor than the lead strategist. If he did anything wrong, it was on the advice of his staff, and for the stability of the nation.

On election night 1988, Mr. de la Madrid said, the secretary of the interior advised him that the initial results were running heavily against the PRI. The public demanded returns, Mr. de la Madrid wrote. And rather than giving them, the government lied and said the computer system tabulating the votes had crashed.

This was the advice to Mr. de la Madrid from the president of the PRI: "You have to proclaim the triumph of the PRI. It is a tradition that we cannot break without causing great alarm among the citizens."

As midnight approached, Mr. de la Madrid learned that the leading opposition candidates were preparing to add more confusion to the outcome of the election by each declaring himself the winner. The PRI, he decided, had to pre-empt them, and without any official vote count, the president of the PRI declared his party the winner. A beleaguered Mr. Salinas did not show his face until the next day.

"The electoral upset was a political earthquake for us," Mr. de la Madrid wrote. "As in any emergency, we had to act because the problems were rising fast. There was not a moment for great meditation, we needed agility in our response to consolidate the triumph of the PRI."

Three years later, in an alliance between the PRI and the conservative National Action Party, the Mexican Congress ordered the ballots of the 1988 election burned, and the only hard evidence of the fraud committed that July night went up in smoke.