It is on television, on radio, in the newspapers and on the lips of Mexicans everywhere: The latest campaign slogan by a leading presidential candidate is so clever and outrageous that in just two days, it became the symbol for how much electoral politics have changed in Mexico.

"Screw the System!" is perhaps the closest printable translation of the new advertisements by Roberto Madrazo, a maverick state governor from the ruling Institutional Revolutionary Party (PRI) who is running for the presidential nomination in his party's first open primary.

With aggressive attacks on his own party and its presumed favorite candidate, Madrazo is turning the traditionally staid and controlled world of high-level PRI politics on its head. In the process, he is demonstrating the power of the media in galvanizing Mexican voters and transforming electioneering in a country unaccustomed to such open or bruising campaigns.

"We've not seen anything like this in the past, and to me that means we're going to have a real campaign for the first time ever," said political columnist Sergio Sarmiento.

The frontal attack on the PRI and Francisco Labastida Ochoa, the former interior minister believed to be President Ernesto Zedillo's favorite, has stunned the party hierarchy and caught Labastida flat-footed. The ruling party's presidential candidate has been handpicked by the outgoing president for the seven decades that the PRI has controlled Mexico. So its first primary Nov. 7 has unleashed rivalries never before so publicly exposed.

In a nation that prides itself on politeness, Mexicans are alternately astounded and entertained by the unfolding campaign.

"They did something that outraged people, created a commotion and a controversy," said Carlos Lopez, a Mexico City business executive. "But it takes away from the stature of a presidential candidate. This is locker room talk."

But with just three months remaining until the primary, Madrazo and his sassy, anti-establishment campaign have caught fire, while the campaign of Labastida, who is viewed as the stodgy candidate of the system, has yet to ignite. Analysts said his handlers seem not to recognize the power of the electronic media or how to use it.

"Labastida is perceived as the guy who has to stick to the rules because he's perceived as the official candidate," said a Mexico City political consultant. "But I can assure you that no one sitting around the dinner table is going to be discussing Labastida's high-minded ideas. They'll be talking about Madrazo's low and vulgar phrase, and that's what you want in marketing, for people to talk about your product."

Labastida campaign officials said they are preparing to introduce a more restrained--and, they hope, presidential--slogan: "I have the character. Together we have the force." The candidate will make veiled references to questions regarding Madrazo's links with disgraced former president Carlos Salinas de Gortari and well-publicized accusations of financing irregularities in Madrazo's 1994 race for governor of the southern state of Tabasco.

"Labastida has a different profile. People feel secure when they see him," said one of his campaign advisers. "Madrazo is so aggressive it will boomerang against him."

Many analysts say the July 2000 presidential election will be one of the toughest ever for the PRI, which has held power continuously longer than any other political party in the world. Partly in response, Zedillo and other reformers have pushed for internal changes, including the primary, to make it more democratic and attractive.

Perhaps one reason the tone seems raucous is that the PRI is the only Mexican political party with such an open and contested primary process. The candidates of the two main opposition groups--the center-left Democratic Revolutionary Party and the center-right National Action Party--are virtually ensured, although they are discussing a coalition candidate.

In opting for a primary, Zedillo abandoned the traditional prerogative of selecting the PRI's next presidential nominee, which--because of the party's unbroken winning streak--was tantamount to naming his successor. The selection process is known here as the dedazo, or, literally the "fingering" of the candidate.

In Spanish, Madrazo's new campaign slogan cleverly rhymes his name with the fingering--Dale un Madrazo al Dedazo--and plays off the widely held view that Zedillo, while championing democracy, has delivered a secret dedazo that will deliver the PRI nomination to Labastida.

Political analysts said the brilliance of the slogan is its multiple meanings. Literally, dale madrazo means to give a strong punch. But to Mexicans, the sentiment behind the words is far stronger and more vulgar. And because the dedazo is such an institution here, the slogan also refers to the fingering process, the entire political system or even Labastida himself.

"In terms of political belligerence, it's a very well constructed slogan," said political columnist Raymundo Riva Palacio. "For the ruling elite class, the thinkers, it sounds trivial. But right now, the campaigns aren't looking for the intellectual elites. They're looking for PRI votes, and this is the kind of speech that appeals to them."

The ads have generated controversy, word of mouth and a bonanza of free press coverage that money cannot buy.

"Our strategy was to make a lot of noise with the first ad and to position Roberto as a rebel with a cause in the PRI, and it has worked beautifully," said the man who dreamed up the slogan, Carlos Alazraki, the strategic planner and creative director for Madrazo's campaign.

"The PRI is the only party that is allowing people [to choose] their nominee," said the Mexico City political consultant. "These guys are hitting each other . . . but they are presenting ideas, and they are giving credibility to themselves and the process."

CAPTION: Roberto Madrazo is seeking the presidential nomination of the ruling Institutional Revolutionary Party.