The leader of National Action Party (PAN) in the capital, Carlos Gelista, accused the mayor of turning city hall into "a campaign headquarters" and using city resources to organize the rally.

"The city has been left without a mayor," Gelista said. "What it has is not an administration, but a campaign committee." Deputy Mayor Alejandro Encinas denied that Sunday's mass demonstration was an official rally promoting López Obrador as the candidate of the Party of the Democratic Revolution (PRD) for the 2006 presidential race. He also denied that city funds were used to pay for organizing the rally.

While the mayor has refused to officially say he wants his party's presidential nomination, many analysts interpreted Sunday's rally as the beginning of López Obrador's campaign.

López Obrador was joined in the rally by PRD national and state leaders, lawmakers and governors.

Rather than rail against "the forces of darkness" the mayor has said are out to ruin his chances to seek the presidency, he presented a national program calling for a reactivation of state supports to the economy.

The 20-point "alternative national project" the mayor presented for debate was widely regarded as an unofficial campaign platform by many political analysts.

"Yesterday we saw the emergence of new leadership in a Mexican leftist party," political analyst Salvador García Soto said of the massive turnout in support of the mayor.

Most estimates put Sunday's crowd, which jammed the heart of the capital, at around 200,000 to 300,000.

Members of the PRD said it was the largest rally for a leftist politician in recent history.

López Obrador is awaiting a decision by legislators on whether he should be stripped of immunity from prosecution for disobeying court orders to halt construction of a public street on privately owned land.

The mayor is the favorite in the polls for the 2006 presidential elections, but he could be barred from running for president if he has to face trial.

With López Obrador, "a new leader is emerging who unites the forces of the left," said García Soto, explaining that with this "show of force," the mayor presented a clear message: "he is capable of mobilizing the people."

The analyst said President Vicente Fox must be aware of the situation because a civil conflict could ensue if the masses come to López Obrador's defense in the event that he has to stand trial.

The Mexico City mayor's case is currently in the hands of a legislative commission which must decide whether or not to strip him of his immunity, but García Soto believes that Fox must look for other solutions to the case.

Before Sunday's march, legislators from other parties said they would not buckle under the pressure of street protests, and if it comes to voting on López Obrador's case, they would vote in favor of stripping him of his immunity from prosecution.

López Obrador used Sunday's demonstration as an opportunity to present his economic, political and social platform for the country, which includes reducing social inequalities and increasing the rule of law.

"Contradicting what his critics predicted, López Obrador did not call for his supporters to set the country on fire," said PRD Sen. Jesus Ortega. "He spoke out for the beginning a great national debate."

Political analysts criticized the plan, however, especially since the mayor has not elaborated on how he plans to implement his ideas.

No one "could oppose the catalogue of good intentions announced Sunday by the head of the capital's government. But if this is a new national plan, a lot more must be demanded of it, beginning with something basic: how and with what (resources) these goals will be achieved," analyst Jorge Fernández Menéndez said Monday in his column "Razones," in the daily Milenio.

But García Soto said it was important that the mayor simply present his political platform after having been criticized for not having one.