President Carlos Salinas de Gortari has announced sweeping measures to combat Mexico City's legendary smog, a thick brown soup rated by ecologists as the world's worst and potentially the most deadly.

Air quality is so poor in the world's most populous city that mere breathing has become a hazardous activity - roughly the equivalent of smoking two packs of cigarettes a day.In response to warnings by ecologists that many Mexico City residents may die of smog-related ailments this winter, Salinas on Wednesday announced restrictions on driving, an extension of school vacations, bans on certain types of incineration and other measures aimed at alleviating the problem.

"There will be people who are opposed to these measures, but this is about protecting the health and well-being of the residents of the Valley of Mexico," Mexico City Mayor Manuel Camacho Solis said following the announcement. "If we just sat back and crossed our arms, we would be committing the worst mistake of all."

Political parties of all stripes have promised to put aside their differences to tackle the problem before the crisis worsens.

On Tuesday, Jose Angel Conchello, a delegate for the conservative National Action Party in the House of Representatives, voiced the desperation felt by many of the city's 20 million residents, saying, "Mexico City is a time bomb, and if urgent measures are not introduced this bomb will explode."

In his inauguration speech Dec. 1, Salinas pledged an all-out war on pollution, saying it was one of the city's worst problems. "The people's health is in a state of crisis," he said.

The measures announced Wednesday include extending school vacations from Dec. 15 until the beginning of February, restricting the use of private vehicles on days when pollution is particularly bad and prohibiting the burning of tires and certain chemicals in winter.