The previous day, bowing to the demands of 1 million demonstrators, Mexico's two biggest political parties had ended a monthslong legal maneuver aimed at preventing him from running.

"They didn't even take one feather off the rooster," a grinning López Obrador crowed. "They wanted to pluck him, but they couldn't."

Indeed, the effort to block López Obrador's presidential bid on what was widely perceived as a trumpedup criminal charge has backfired, creating one of the biggest political embarrassments in recent Mexican history and clinching the mayor's front-running position in the July 2006 elections.

But while López Obrador has emerged as the darling of the masses, the question reverberating on both sides of the U.S.Mexico border is whether he can gain the confidence of a White House already concerned about Latin America's lurch to the left.

"The knee-jerk reaction is to paint him with a broad brush as a leftist, to stereotype him with the Chávez label or the Lula label," said Armand B. Peschard-Sverdrup, a Mexico expert at the Center for Strategic and International Studies in Washington, D.C. "But it's too early to say what kind of president he'd be."

Peschard-Sverdrup was referring to Venezuela's leftist strongman Hugo Chávez, a thorn in Washington's side, and Brazil's Luiz Inacio Lula da Silva, a former union leader who has forged a workable, if brusque, relationship with the United States.

They are among an array of leftist presidents, national legislators and local leaders who have won office across the region as voters reject free-market policies that have failed to stem growing poverty. But unlike Mexico, none of those countries share the United States' southern border.

The usually brash López Obrador, known here simply as AMLO, already has sought to assuage the United States' concerns, insisting he is "neither a populist nor a neo-liberal."

"What we are proposing is a change in economic policy, but that does not mean implementing radicalism," he said Friday.

Still, he acknowledged, "the left is at the heart" of his policies, which aim to distribute more resources to "the poor, the weak and the forgotten."

For now, Washington is adopting tactful diplomacy. Asked in March about a possible López Obrador presidency, President Bush pledged: "I am willing to work with whoever is chosen by the Mexican people."

That may indeed be López Obrador: His popularity in Mexico City has jumped to 84 percent from 76 percent in just three months. Nationally, he leads his closest presidential rivals by at least 11 points.

He has remained Spartan in his personal habits since becoming mayor in 2000, driving a subcompact car and living in a moderateincome apartment complex.

But he has lavished funds on dazzlingly high-profile projects such as double-decker highways and old-age homes for elderly prostitutes. He also has forged alliances with the business community to reduce crime and restore the crumbling historic center.

Though López Obrador is a natural for leftist Mexico City, political analysts predict he'll have to moderate his stances to broaden his support; nationwide, his Party of the Democratic Revolution commands only 20 percent of the vote.

Otherwise, he'll continue to face opposition from the likes of Claudio X. González, one of Mexico's most powerful business leaders, who last week slammed the free-spending mayor as "a leftist who is retrograde and dinosaur-like, and who will leave Mexico in bankruptcy."

Indeed, the biggest concerns about López Obrador, who speaks no English and has never visited the United States, are likely to come from Wall Street, not the White House.

López Obrador has suggested restructuring Mexico's foreign debt and adamantly opposes privatizing the country's oil and electric industries. But political analysts believe he has neither the desire nor the ability to dismantle the economic interdependence between Mexico and the United States created by the 11-year-old North American Free Trade Agreement.

López Obrador sees economic development as the key to stemming the flood of undocumented Mexicans into the United States, and describes improving the rights of immigrants as "the principal topic in the bilateral agenda" with his northern neighbor.

How López Obrador would press that concern is an oft-repeated question. "I could see López Obrador organizing rallies of undocumented immigrants to pressure Washington," mused George Grayson, a Mexico expert at the College of William and Mary in Williamsburg, Va., who is writing a biography of López Obrador.

That's how López Obrador thwarted efforts by President Vicente Fox's Political Action Party (PAN) and the PRI to charge him with ignoring a court order in a minor dispute over the construction of a hospital access road. Mexican law bars anyone charged with a crime from running for president.

At López Obrador's behest, thousands of Mexicans hung banners from their shops and homes declaring, "AMLO, you are not alone!" Then they took to the streets for a series of protests demanding the government drop its investigation, culminating in a 1-million-strong march here April 24.

AMLO supporters were particularly outraged because public officials in this notoriously corrupt nation routinely evade prosecution for far greater offenses.

In capitulating, an embarrassed Fox let go his attorney general and appointed a replacement who gingerly concluded Wednesday that no charge existed for the alleged crime.

In what was widely viewed as a scramble to salvage his reputation, Fox met Friday with López Obrador. Mexico City-based political analyst Federico Estevez likened the talks to "the Japanese emperor signing the unconditional surrender on the USS Missouri" that ended World War II.

"With enemies like that," said Grayson of Fox and the PRI, "López Obrador doesn't even need friends."