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.''