MEXICO CITY — WHEN Mexico's Congress approved a 50 percent sales tax increase earlier this month as the keystone of President Ernesto Zedillo Ponce de Leon's emergency economic plan, legislators from the ruling Revolutionary Institutional Party (PRI) whooped in exaltation.
The cheering was not for the measure itself, which is very unpopular with the public; in fact, two PRI legislators voted against Mr. Zedillo's plan -- a historic first. Instead, the celebration was an expression of relief for the beleaguered political system -- and perhaps a last hurrah for a virtual one-party rule under pressure to change.
Mexico today presents a picture of a cracking old order, with intra-party power struggles capped by assassinations, a disgraced former president, and high-level officials on the take from business and drug empires.
But while the instability keeps Mexicans guessing what's coming next and makes foreign investors leery, it is opening the door to a more open and pluralistic political system.
Mexico's transition is not so different from those of other single-party regimes in other countries.
''What we are seeing is the deterioration of an authoritarian regime and the weakening of the elites of the ruling group,'' says Sergio Aguayo, a political analyst at the Colegio de Mexico here. ''Mexico is finally experiencing what happened in Spain, Nicaragua, the Soviet Union.''
Complicating Mexico's transition is the fact that it is taking place during an economic tailspin.
When Zedillo was elected last August, many analysts concluded that Mexico's economy, then thought to be poised for substantial growth, would virtually take care of itself while the new president addressed the country's pent-up social and political demands. But Mexico's economic collapse was partly the result of a political system that allowed an all-powerful president to refrain from addressing a deteriorating economic performance.
''The economic crisis is one of the manifestations of the old system's collapse,'' says Mr. Aguayo.
Among the questions facing Mexico now are whether the current transition will leave the country more stable and governable, what role the once all-powerful PRI still has to play -- either within the transition or as a force thwarting it -- and whether Zedillo, an undistinguished economist and bureaucrat never destined for the presidency in the PRI's designating system, is strong enough to manage the country's intertwined crises.
With the country facing one of its most difficult moments of this century, Zedillo is attacked both inside and outside Mexico for not being up to the task he faces. He is no Abraham Lincoln, he is no Winston Churchill, writes political analyst Raymundo Riva Palacio this week. Yet while that may be true, Zedillo has also shown he can make decisions pushing Mexico toward change.
In what may have been his most far-reaching decision so far, Zedillo broke the PRI's lock on the presidential Cabinet by naming a member of the opposition National Action Party (PAN) to head the federal justice department. That appointment grows in significance as Zedillo continues to emphasize judicial reform as a key to Mexico's governability, and as the investigations of high-level political assassinations point higher within the PRI.
But Zedillo has taken other steps that acknowledge the demands of a more pluralistic society. Carlos Castillo Peraza, president of the PAN, lists Zedillo's opening of a dialogue with the major opposition parties to formulate an electoral reform with clearer democratic guarantees, and the creation of a multiparty commission to address the conflict in Chiapas, as evidence that Zedillo conceives of the presidency differently from his predecessors. Before leaving office, former president Carlos Salinas de Gortari said he ''neither saw nor heard'' the political opposition.
Elections in February in the important state of Jalisco that were judged clean and that gave the state a PAN governor and its first-ever opposition government are another important bellwether.
''We are witnessing the emergence of new forces that are independent of the old ruling groups,'' says Aguayo, pointing to independent democratic watchdogs, wide-ranging private organizations, the Zapatista guerrillas in Chiapas, the private business sector -- and the PAN, now solidly Mexico's strongest opposition party.
With no democratic tradition to guide it, the PRI is degenerating into a group of warring interests and local rulers seeking to hold on to what power they can, many observers agree. Yet while some PRI members insist the party includes modernists who want genuine democratic reform, even they are not convinced that the PRI's place in a changing Mexico is assured.
''If the PRI doesn't reform itself, it is going to disappear,'' says Martin Alberto Sanchez, coordinator of Democracy 2000, an organization of PRI members pushing internal reform. One of the central changes the group wants is adoption of a democratic selection process for all PRI candidates in time for congressional elections in 1997. In most cases local PRI leaders now designate their candidates, while the president hand-picks his own predecessor.
But even this change will not be easy for the PRI. ''There are a lot of very powerful interests opposed to the kind of changes we seek,'' says Mr. Alberto. He says the months before the PRI's national assembly in June will reveal the party's inclination to reform.
Perhaps the PRI's greatest problem is that it has no strong national leadership to guide its transition, with the leaders it looked to a year ago all out of the picture: former presidential candidate Luis Donaldo Colosio and rising party reformer Jose Francisco Ruiz Massieu both assassinated, Mr. Salinas rejected and in at least temporary exile, and former Mexico City mayor and reformer Manuel Camacho Solis effectively shoved from the party nest.
That has left the PRI still powerful -- enough to strike a reflex and vote in Zedillo's tax hike -- but with little sense of direction.
Still, few observers see the PRI's troubles sinking Mexico into chaos. What Mr. Castillo Peraza calls the PRI's ''Yugoslavization'' is ''a problem for the country, but not to the point of threatening [Mexico's] general governability,'' he adds.
Thinking that the PRI's challenges put the country's stability in question ''ignores the other forces emerging in Mexico,'' he says.