The Supreme Court agreed yesterday to hear a case about whether the Los Angeles area can go beyond the federal Clean Air Act to impose strict anti-pollution rules on buses, taxis, garbage trucks, airport shuttles, and other vehicle fleets. Oil companies and engine manufacturers challenged a rule issued in 2000 by the South Coast Air Quality Management District that requires owners of public and private fleets with at least 15 vehicles to buy low-emission or alternative-fuel vehicles when replacing or expanding their fleets. Old, diesel-burning fleet vehicles have been a significant contributor to Southern California’s infamous air pollution problems; one study found that diesel exhaust was responsible for 71 percent of cancer risk from airborne materials in the L.A. area. The court’s decision will have national implications because other states often follow California’s lead in cracking down on sources of air pollution. The case will be heard this fall.