MEXICO CITY, AUG. 14 -- Mexico's governing party, responding to widespread criticism and internal dissent, surprised the nation last night by announcing six possible presidential candidates, ending a tradition of hiding contenders from the electorate.

Jorge de la Vega, president of the Institutional Revolutionary Party, known as PRI, announced the "transcendental step in the history of our party" on television last night, reading the list of the six candidates who could succeed President Miguel de la Madrid in July 1988 elections.

PRI has governed Mexico since the party's formation in 1929, winning every presidential, gubernatorial and senatorial race. But it has been under growing pressure in recent years to open itself to more pluralistic procedures.

"It is the first time in almost 60 years . . . that a measure of this nature has been taken, and it is an unequivocal indication that fresh winds are blowing over the PRI," said an editorial today in the influential newspaper Excelsior.

In recent decades, the Mexican president, who can govern for only one six-year term, has personally chosen his successor.

Others saw the move as an effort by PRI to shore up its image without making any substantial concessions, although some opponents said the change could actually prove significant. During previous successions, tradition has forbidden presidential hopefuls from openly declaring their candidacy or stating their own views on national matters.

The practice has led to growing criticism of the tapadismo, or veiled system, in which the candidates campaigned behind the scenes until the president selected one, who was then announced to the nation as the party's choice.

Arnaldo Cordova, a federal lawmaker for the Unified Socialist Party of Mexico, the nation's largest leftist party, said the announcement was "an interesting innovation, although with very obvious limitations, because the phenomenon of tapadismo continues."

Cordova conceded it "was an advance, because we can listen to the possible candidates, but the country needs more than that."

In previous administrations, the period before the PRI candidate was announced has been one of tension and uncertainty, with businessmen and labor leaders, and often Mexicans in general, fearful that an unexpected choice could lead the nation in unforeseen directions.

The PRI has also been facing a revolt from leftist and liberal PRI leaders who form the so-called "Democratic Current." They nominated Cuauhtemoc Cardenas, former governor of Michoacan and son of Lazaro Cardenas, one of the most popular presidents in history, to be one of the PRI candidates. Cardenas, however, was not on the list of PRI candidates mentioned by de la Vega.

The main PRI candidates include Interior Minister Manuel Bartlett, Energy Minister Alfredo del Mazo, Budget Minister Carlos Salinas de Gortari, Mexico City Mayor Ramon Aguirre, Federal Attorney General Sergio Garcia Ramirez and Public Education Minister Miguel Gonzalez Avelar.

De la Vega said that the six candidates were chosen after his visit to most of the 31 Mexican states, where he met with leaders and activists of the three main groups within the PRI: workers, peasants and the middle class.

Mexico is currently undergoing its worst economic crisis in decades, with inflation for the past 12 months at 133 percent and unemployment and underemployment at 50 percent.