The image-makers in Mexico's presidential primary campaign told Francisco Labastida Ochoa to shed his coat and tie, and by the way, don't smile--look serious. Media consultants pushed a rival candidate, Roberto Madrazo, to bolster his rebel image by going for the jugular in the toughest political advertisements ever seen on Mexican television.

But when it came to Vicente Fox's boots, the focus groups were divided. While the folksy cowboy look is an attention-grabber on the campaign trail, some warned that the pointy-toed, brown calfskins just are not presidential enough for the executive mansion in Mexico City.

Mexico's most openly contested presidential election in 70 years has spurred a revolution in political campaigning. Facing an increasingly sophisticated electorate and unprecedented competition in a country where the president has hand-picked his successor for most of this century, candidates in Sunday's primary and next July's general election have embraced television and packaging by strategists and pollsters from the United States.

"We are going more and more the route of the United States," said Fox, a former state governor and Coca-Cola Co. executive who is the right-of-center National Action Party (PAN) candidate for president in the general election next July 2. "Have charisma and look good on TV, and you can become president."

That is an improvement, in Fox's view. As an opposition candidate in a nation that has been ruled by a single party for seven decades, Fox said, "With the old system here in Mexico, we didn't have any chance. Like in the Roman circus, we were thrown into the arena with our hands tied behind our back with no money, no access to media and no possibility of winning. Of course I prefer what it is today. I enjoy competition."

Political analysts note that in past Mexican elections, the ruling Institutional Revolutionary Party, or PRI, maintained power by using the government political machine and ballot fraud. In that light, they say, the changes benefit voters.

"In a country like Mexico it's actually a step forward," said Robert A. Pastor, who monitored Mexican elections for more than a decade as Latin America director for the Carter Center, which dispatches election observers around the world. "The focus groups and public opinion surveys are the first signs that politicians are trying to respond to the people."

This year, President Ernesto Zedillo became the first sitting PRI president to forgo anointing his party's presidential candidate, instead opening the process to a primary. At the same time, he pushed electoral reforms through the Mexican congress giving opposition parties--already gaining strength at local and state levels--a better chance to woo voters for the presidency.

"Now you have to go into a competitive political marketplace and present yourself," said Stanley Greenberg, a former campaign pollster for President Clinton who is working for Labastida. "It shows people that elections do matter. It brings out the best in candidates, but also hurts those candidates who don't respond to what people are looking for."

Such competition also may force change in the kind of politician who becomes a candidate--and thus president. The powerful but often ponderous party insiders who made it to the Mexican presidency under the old system now are likely to be replaced by more telegenic party salesmen.

Labastida, until recently a Zedillo cabinet member, is widely viewed as Zedillo's favored candidate for the PRI nomination over three other contenders. Nevertheless, the reforms have forced all candidates to expand beyond Mexico's traditional electioneering methods of busing party loyalists to rallies in town squares and plastering village walls with propaganda.

"Today you need much more presence in the media because the people are more critical; it's a more informed society," said Madrazo, who has bought the most television advertising of the four PRI candidates.

"Definitely, this is a media campaign," agreed a Labastida campaign official. "We're testing everything as never before--even the color of his shirt. The focus groups tell us people like him to be more serious in pictures rather than smiling. They don't want to see a guy smiling when everybody's worried about crime and security. And they want to see him without a jacket."

But with a political system that nurtured few homegrown consultants, most contenders are using U.S. advisers and pollsters. Strategist James Carville, along with pollster Greenberg--the team that orchestrated Clinton's 1992 presidential campaign--are advising Labastida. Madrazo's campaign has hired consultant Zev Furst and Clinton's 1996 campaign pollster Douglas Schoen. Fox has consulted with Clinton's former campaign strategist Dick Morris.

In a country where U.S. advisers would be seen as a political liability by a nationalistic electorate, most Mexican candidates do not publicly acknowledge their U.S. consultants, usually hiring them as subcontractors through Mexican counterparts.

In an illustration of how critical electronic media has become, the Mexico City daily Reforma publishes a daily box score with the number of seconds each candidate received on the previous night's news programming and paid advertising. Over the last two months of the campaign, Labastida received 35 percent more time on television news shows than Madrazo.

To compensate, Madrazo has bought up to 30 percent more television and radio air time than Labastida in recent weeks, according to the Reforma survey.

Madrazo this week aired an advertisement showing an actor impersonating reviled former president Carlos Salinas de Gortari as he holds a puppet with Labastida's face. In his counter-ad, Labistida flashed a photograph of Salinas standing next to a young Madrazo, whom he endorsed in campaigns for the senate, house of deputies and governor of the southern state of Tabasco.

Candidates are also experimenting with a cheaper alternative that is accessible to only a small fraction of Mexican voters--the Internet.

"It's become one of the pillars of the campaign--there's been explosive growth," said Luis Alberto Bolanos, webmaster for the Fox campaign.

Madrazo has used the Internet to host video conferences and electronic chats with his campaign offices scattered throughout the country, according to Manuel Zendejas, the campaign's Internet coordinator. But all the PRI candidates took down their sites at the close of official primary campaigning Wednesday night, abiding by rules that consider them part of the campaign.

Correspondent John Ward Anderson and researcher Garance Burke contributed to this report.

CAPTION: A TV ad mocks candidate Francisco Labastida Ochoa, who is portrayed as the puppet of unpopular former Mexican president Carlos Salinas de Gortari.