THE NATION that poet Octavio Paz once accused of "falling asleep for a hundred years" has finally awakened. In a mere five years, a Mexico tottering on the verge of bankruptcy has lifted itself from the brink of financial ruin, proclaimed itself a "regional power" and publicly crossed swords with Uncle Sam on the issue of El Salvador. Bust has turned to boom, and Mexico is now building its tallest buildings, making its first military purchases in years, and even considering an ambitious nuclear-power program. One government publication proudly proclaims that Mexico "is no longer a sleepy, south-of-the-border neighbor." In fact, everyone in Mexico City today seems to be in a hurry; the siesta, for all practical purposes, has ceased to exist.

Economic success has brought a new international self-confidence. It is the Mexican government that is offering to play the leading role in negotiating a solution in El Salvador. The joint declaration with France, recognizing the legitimacy of Salvador's revolutionary movement, was a direct affront to President Reagan's Central American policy and drew the wrath of most conservative powers in the region. And as an acknowledged leader of underdeveloped countries, Mexico will host next month's historic conference on North-South relations.

The dramatic changes taking place in almost all aspects of Mexican life can be explained by a single, three-letter word: oil. The discovery of vast petroleum reserves in the country's southeastern marshlands has captured the attention of industrialized nations seeking to insulate themselves from the effects of another Middle Eastern boycott. Today, Mexico is the world's fourth largest oil producer, with reserves exceeded only by Saudi Arabia. And with every announcement of an increase in reserves, the expectations of Mexico's 70 million people rise to new heights.

Gas is cheap in Mexico City--about 40 cents a gallon-but the Mexicans who fill up at stations run by the state-owned oil monopoly, Petroleos Mexicans (PEMEX), are greeted by signs promising not only low costs but "better schools and better Mexicans." The first underdeveloped country in the world to nationalize its oil industry, Mexico is proud that PEMEX survived a vindictive technology and equipment boycott by the major American oil firms. Today, it ranks as one of the world's largest 500 companies, and there is even talk of PEMEX competing with Exxon by selling gasoline in the southwestern United States.

BUT WHO is benefitting from Mexico's vast oil resources? Though the government maintains it is the average Mexican, the trickle-down philosophy it employs has done little, if anything, to rectify one of the most skewed income distributions in the world. Last June, at a Kennedy School forum, Mexico's Ambassador to the United Nations, Oscar Gonzales, acknowledged that income distribution in Mexico--where the top 30 per cent of the society enjoys 70 per cent of the income--is less equitable than in El Salvador. And economic data show that the disparity in Mexico has actually worsened during the "development" process. Unemployment estimates range as high as 50 per cent, while the cruel perversity of the existing system permits only those who have jobs to receive social security.

Mexico is a classic example of dual economic development. Two societies compete within one nation: the affluent versus the destitute. To use one commentator's analogy, Mexico is a Sweden imposed on an Indonesia. The "Sweden" has an active economy of its own and constitutes a sizable domestic market for consumer goods, without having any great effect on the "Indonesia."

The peasants who live in Mexico's southeast are the Mexicans closest to their nation's oil wealth, yet least likely to receive a share of it. Those living outside Coatzacoalcos, an oil boom town, complain bitterly about the arrogance of PEMEX, which can unilaterally expropriate their land. They say that the sulfur in the air corrodes the tin roofs of their shacks, and that their cows have died from drinking contaminated water. The land has become less fertile, with crop yields declining by as much as 30 per cent.

The peasants have few alternatives but to vote for the Partido Revolucionario Institucional (PRI), the party that has ruled Mexico without opposition for 50 years. To maintain its hegemony, the PRI minimizes political mobilization among the populace. Promises of government attention, combined with a foreign policy that even the most dedicated leftists cannot impugn, have traditionally kept activists quiet.

Every six years, the PRI's presidential candidate is handpicked by his predecessor before a meaningless election. This year's choice, Programming and Budget Minister Miguel de la Madrid, is a Kennedy School-educated, free-market conservative who says he favors closer cooperation with the United States. He will work to attract foreign investment and to increase the production of luxury goods. Though de la Madrid and his party can be praised for giving Mexico a half century of "stability" while much of Latin America has been engulfed in turmoil, it is this same party that has tolerated the existence of an "Indonesia" when the "Sweden is at its most prosperous.