Mayor Gavin Newsom is competitive about many things, garbage included. When the city found out a few weeks ago that it was keeping 70 percent of its disposable waste out of local landfills, he embraced the statistic the way other mayors embrace winning sports teams, improved test scores or declining crime rates. Workers sort plastics at the San Francisco Recycling Center. The city, with 7,800 tons of waste a day, keeps 70 percent of it out of landfills. Mayor Gavin Newsom is shooting for 75 percent. But the city wants more.