A defeat in court of the EPA’s plan to postpone methane standards for oil and gas wells could bolster challenges to delays of emissions limits for landfills and regulations for new chemical plant security.

A federal appellate court’s ruling that the Environmental Protection Agency lacked the authority to halt the oil and gas methane emissions standards for 90 days could be a signal the agency’s regulatory rollback is in line for additional legal scrutiny, environmental advocates said. While the decision...