WASHINGTON — In its first major regulation since the election, the Obama administration on Friday imposed a new air quality standard that reduces by 20 percent the maximum amount of soot released into the air from smokestacks, diesel trucks and other sources of pollution.

Environmental Protection Agency Administrator Lisa Jackson said the new standard will save thousands of lives each year and reduce the burden of illness in communities across the country, as people “benefit from the simple fact of being able to breathe cleaner air.”

As a mother of two sons who have battled asthma, Jackson said she was pleased that “more mothers like me will be able to rest a little easier knowing their children, and their children’s children, will have cleaner air to breathe for decades to come.”

Announcement of the new standard met a court deadline in a lawsuit by 11 states and public health groups. The new annual standard is 12 micrograms per cubic meter of air, down from the current 15 micrograms per cubic meter.

The new soot standard has been highly anticipated by environmental and business groups, who have battled over the extent to which it would protect public health or cause job losses. The EPA said its analysis shows the rule will have a net benefit ranging from about $3.6 billion to $9 billion a year.

A study by the American Lung Association and other groups said the new standard will save an estimated 15,000 lives a year — many in urban areas where exposure to emissions from older, dirty diesel engines and coal-fired power plants are greatest.