MEXICO CITY, Mexico (AP) -- Mexico City's leftist mayor led more than 150,000 demonstrators in a march Sunday to protest efforts to impeach him, an issue his supporters say threatens Mexico's political stability and pits "those on the bottom" against "those on top."

Protesters brought in by hundreds of buses from nearby states mingled with local supporters of Mayor Andres Manuel Lopez Obrador, a leading contender in the 2006 presidential race whom critics liken to Hugo Chavez, the populist president of Venezuela.

Although Lopez Obrador denies similarities with the one-time Venezuelan coup leader, he rallied his followers with fighting words, saying he represented "los de abajo," roughly "the underdogs," the title of a famous novel about peasant rebels in Mexico's 1910 Revolution.

Although he didn't declare his candidacy, Lopez Obrador laid out a campaign platform that envisioned a return to a more self-sufficient, oil-based economy and a renegotiation of part of the public debt, measures Mexico tried two decades ago.

"We have to recover the best of Mexican history, that's where Mexico's character is," Lopez Obrador told a cheering crowd. "We should return to the policy of state support that has been practically eliminated by free-market policies. We have to support industry."

Much of Lopez Obrador's speech -- "We favor a responsible, productive private sector with social commitment" -- sounded strikingly like the 1970s rhetoric of the former ruling party.

Lopez Obrador has stoked class passions, saying before the march: "The ones on top aren't going to come. They just dine and drink fine wines, and make decisions that hurt the little guy."

Federal prosecutors have filed a case to remove Lopez Obrador's official immunity from prosecution -- a move that would bar him from running in 2006 -- because they say he ignored court orders in an obscure land-use case in which the city allegedly infringed on private property.

Lopez Obrador argues that many other officials have ignored similar court orders, but that he was singled out for prosecution because his opponents -- purportedly including President Vicente Fox -- want to knock him out of the 2006 race, which he leads in polls of potential voters.

Many in the march -- made up of farmers from Lopez Obrador's state of Tabasco and local neighborhood groups, street vendors and retirees' organizations -- vowed to defend the mayor's presidential hopes by any means necessary.

"The people are going to start a rebellion" if Lopez Obrador is impeached, pledged Rigoberto Benetiz, a 60-year-old farmer who led a group of protesters from the southern state of Guerrero. "The people will go into the streets."

The rebel rhetoric isn't limited to just some supporters; top officials of Lopez Obrador's Democratic Revolution Party, the PRD, have threatened political instability and quite possibly violence if Lopez Obrador is impeached.

"This could lead the country into serious and grave conflicts," said PRD-affiliated Gov. Leonel Cota of Baja California earlier this month, noting some supporters could take "the route of arms, of mobilization, of confrontation" if Lopez Obrador is impeached.

The mayor has portrayed himself for months as the victim of a political conspiracy, at first in response to a corruption scandal involving videotapes of city officials accepting cash from a businessman and spending lavishly in Las Vegas.

Despite his fiery rhetoric and populist handout programs, Lopez Obrador has denied any similarity to Chavez. "I'm not like him," the mayor said, noting Chavez has a military background, while he was a political science major.

Lopez Obrador has built his popularity on his familiar, humorous speaking style and handout programs that have given Mexico City residents everything from free school supplies to supplementary old-age pensions.

He has also launched ambitious roadwork programs, but critics say his free-spending style has caused the city's debt to balloon.

The demonstration filled Mexico City's central plaza, and media outlets estimated that between 150,000 and 200,000 people participated. Police do not make crowd estimates.

Sunday's march, though, was smaller than a June anti-crime march that Lopez Obrador has depicted as an attack on his administration. The June march, the largest in recent Mexican history, drew between 300,000 and 400,000 people.

Copyright 2004 The Associated Press.