ECATEPEC, Mexico (AP) _ It's election time in Mexico, and the voters are angry.

``You treat us like dogs!'' a man shouts when a congressional candidate for the long-ruling Institutional Revolutionary Party tries to calm a crowd angry about the lack of water and sewage services.

``We are going to speak with civility,'' chides the candidate, Maria Elena Luna Fernandez, as wind whips up dust from unpaved city streets and sets plastic campaign banners flapping from concrete power poles.

Luna's party, known by its Spanish initials, PRI, has always been able to count on the votes from the crowded Ecatepec neighborhood named for Carlos Hank Gonzalez, a former state governor and perhaps the party's most famed national political godfather.

But as the July 6 mid-term congressional election approaches, many people are running out of patience with the party that has governed Mexico for 68 years.

``I am a PRI-ista to the death,'' says one resident, Maria Elena Ramirez.

But she admits it is becoming harder to support the party after 25 years of waiting for paved streets, adequate schools or reliable water service.

``In the situation we are experiencing, we are collapsing,'' she says.

The PRI has faced great challenges before. Many believe it lost the 1988 presidential election, only to keep power by fraud.

But a series of election reforms has made Mexico's electoral system cleaner and fairer. Polls say the party is in danger of losing control of Congress for the first time, which would be a dramatic turn for a political system accustomed to congressional acquiescence to presidential domination.

Presidential budgets and other proposals would face unheard of challenges if the opposition captured control of Congress. Congressional committees would likely investigate official corruption that in the past was buried.

Some of the toughest battles are being fought in Ecatepec and nearby cities that in many ways are the new face of Mexico.

Suburbs on steroids, they form a grimy belt of working-class poverty around Mexico City. Ecatepec, with 1.5 million people, will soon outstrip Philadelphia in population. Nezahualcoyotl to the east is bigger than Detroit or Dallas. Tlanepantla to the west roughly equals San Francisco's population.

They are growing rapidly with job-seeking migrants from rural Mexico.

In the countryside, there is often little beyond the land _ and many farmers in central Mexico have only an acre or two for their families, none at all for younger sons.

Here there are major factories. By washing windshields, juggling burning sticks or selling gee-gaws and chewing gum for a few centavos at traffic lights, even the most desperate can often scrape by.

Similar gray sprawls of slums have sprung up on cornfields and mountain slopes across the country. Nearly half of all Mexicans now live in cities of 100,000 people or more. Mexico is no longer a rural nation.

And cities are leading a peaceful transformation of Mexico's politics.

Local elections in November turned the PRI out of power in many of the suburbs ringing Mexico City, although it held onto power in Ecatepec.

The PRI trails badly in polls for the July 6 mayoral election in Mexico City itself.

If it loses there, Ecatepec will be the largest city in Mexico governed by the PRI _ and the only PRI stronghold among Mexico's 12 largest cities.

The PRI still dominates the countryside, where it counts on old party loyalties, as well as strong alliances with local political leaders who grant favors to friends and _ in some areas _ repress their critics.

But such ties are slowly breaking down in the cities. Even labor unions, long a pillar of the PRI, are losing their ability to deliver votes from workers angry at a steady decline in the value of their paychecks.

Most Mexicans make less than $7 a day. The economic crisis of 1995 caused a 6.9 percent drop in gross domestic product and devastated workers' buying power, which some studies show to be lower than that of the 1940s.

Middle-class Mexicans and small businesses were stunned by interest rates that suddenly shot above 100 percent a year, plunging many into seemingly impossible debt.

The cheaper peso has helped export industries, which are leading strong growth in the overall economy this year. But even President Ernesto Zedillo says most Mexicans don't feel the benefits yet.

Retail sales _ an indicator of buying power _ fell in the first quarter of 1997. Most new jobs in recent years have been in the informal, non-taxpaying sectors of the economy, which offer little protection and few benefits.

Since 1982, Mexican presidents have steadily dismantled the government-centered economy, selling off state companies, cutting official payrolls, opening the country to imports and encouraging exports. Ever-fewer Mexicans depend on official favors for jobs or land.

Street crime has soared and the country has been shocked by corruption scandals involving the family of former President Carlos Salinas de Gortari. Rumors of high-level drug connections have been fed by the February arrest of the country's anti-drug czar.

Yet the PRI, formed as a party of the state in 1929, has eroded only slowly, and its challengers have been slow to build nationwide bases of supporters. None is strong in every state.

Mexico hasn't seen a peaceful transition of power from one party to another since 1828, says historian Lorenzo Meyer, who notes that election was quickly followed by a coup.

Even now, despite the economic crisis, the ruling party stands a good chance of holding control of Congress. The voting system usually gives a majority to a party that wins just over 42 percent of the overall national vote.

And in the presidential election of 2000, it could win with even less because two strong opposition parties and several smaller factions probably will split the protest vote.

While change has been peaceful in the cities, it has sometimes been sudden and violent in the countryside, where local bosses have often ruled with an iron hand, making peaceful challenges difficult.

The Zapatista National Liberation Army revolted in 1994 and drew heavy support in remote areas of Chiapas state that had long given more than 90 percent of their votes to the PRI.

The shadowy Popular Revolution Army erupted last year in rural Guerrero and Oaxaca states, also PRI strongholds noted for powerful local political bosses.

A recent poll of city dwellers by the polling company Consulta found that nearly 30 percent at least partly approved of the guerrilla-war methods of the Popular Liberation Army.

But the greater threat to the government has been in elections.

Federico Estevez, a political scientist at the Autonomous Technological Institute of Mexico, noted that in some areas less than 30 percent of people polled say they back the PRI.

``That's where the protest went _ to the ballot box,'' he says.