The Chinese government has launched a big millennial campaign to clean up Beijing, with an eye toward the possibility of winning the right to host the Olympics in 2008. More than 1,000 industrial enterprises in the city belch out soot and help give Beijing some of the most polluted, dangerous air in the world; under the cleanup plan, 738 small state-owned factories will be pushed out of the city over the next three to five years. But the government is cautious in talking about the shift because the factories were brought to the capital under the orders of Mao Zedong, who insisted that Beijing must be an industrial stronghold as well as a political and cultural center, and leaders don’t want to give the appearance of repudiating his policies.