The EPA, blocked by two recent court orders from implementing new clean air standards and rules, unveiled a scaled-back approach yesterday for cracking down on polluting power plants and industrial facilities. The approach relies on petitions filed by four states — Connecticut, Massachusetts, New York, and Pennsylvania — that said they could not meet even the previous, more lenient smog standards because of pollution blowing in from other states. Based on those states’ concerns, the EPA said it could force plants in 12 states to reduce their emissions of nitrogen oxides by about 60 percent of what the agency had been aiming for with a new rule that the court suspended. Industries in 10 other states that had been targeted for cuts under the rule would escape new restrictions. Spokespeople for utilities and the coal industry said they would challenge the new approach in court.