BEIJING — Construction will halt, heavy industries will close, and even spray painting will stop in order to clean Beijing’s polluted air for the Olympics — an issue that suddenly has taken a back seat to political protests.

An aggressive plan to temporarily shutter belching steel and chemical plants, cut back emissions by 30% at 19 heavy-polluting companies and stop excavation and pouring of concrete at hundreds of sites around the city was explained yesterday by the city’s Environmental Protection Bureau.

“From the suggestions of experts we think that we need to take these measures to guarantee the air quality of Beijing,” the bureau’s deputy director, Du Shaozhong, said.

The measures are severe and will be in effect officially for two months — July 20 through September 20 — although reports a few months ago suggest some production cutbacks may come even sooner.

Officials also are expected to ban about half of Beijing’s 3.3 million vehicles for the August 8-24 Olympics. Mr. Du said specific details would be announced later.

Yesterday, thousands cheered and some danced with traditional daggers along the Olympic torch’s path through Oman’s capital, Muscat, a festive greeting that contrasted with disrupting protests elsewhere on the flame’s global journey.

Under tight security, about 80 torchbearers ferried the flame down into the heart of this hilly Persian Gulf sultanate’s capital.