A new growth-management strategy unveiled by the Southern California Association of Governments on Tuesday will enable the region to absorb millions of new residents while easing traffic congestion and improving air quality, SCAG officials said. The strategy - a synthesis of longtime growth-management tactics - focuses on reviving down-at-the-heels urban areas with a combination of mixed-use development, new or existing mass-transit lines and denser housing, including loft-style apartments and condominiums.

The Metropolitan Transportation Authority has used the same approach in planning new housing and commercial development along the route of its Red Line subway. But by proposing to extend the strategy to cities in the South Bay and elsewhere throughout a six-county area, SCAG's growth-management plan "points the region in a new direction," said board member Toni Young, who is mayor of the Ventura County city of Port Hueneme.

SSCAG's six-county, 35,000-square-mile planning area includes Los Angeles, Orange, Riverside, San Bernardino, Ventura and Imperial counties. The region has a population of 17 million people that is expected to grow by more than six million by 2030. How the region can grow that much and still meet federal air-quality goals is a problem that has long had planners scratching their heads. Pollution isn't the only concern; the Los Angeles metropolitan area also leads the nation in traffic congestion, and poverty rates are rising alarmingly.

SCAG's latest effort to find a solution, dubbed Compass, was a two-year effort shaped in part by input from local residents. Ultimately, planners concluded that denser housing and commercial development in only 2 percent of SCAG's planning area would keep congestion down, promote economic prosperity and enable the region to meet its air quality goals. The key is channeling much of the new development to areas that are already urbanized but are struggling, such as Hawthorne Boulevard just south of the 105 freeway, said John Fregonese, an urban planner and lead consultant on the Compass project.

By building three-story-high office, mixed-use and retail development in such areas and linking it to new or existing mass-transit lines, 400,000 additional housing units could be built, mass-transit ridership would improve by 50-70 percent and the region could meet its air quality goals, said Mark Paisano, SCAG's executive director. Along with other officials, he emphasized that the single-family homes preferred by many Southern California residents will still be built in many areas.

"This is not a change in the Southern California lifestyle," Paisano said. Nor will the latest plan simply sit on a shelf, he added. SCAG will work with cities around the region over the next six years to develop general plan guidelines that are consistent with the development goals, Paisano said. Change won't come overnight, Fregonese cautioned. "We have some big ideas, but the success of Compass is thousands of small successes built up together," he said.