After a federal-appeals court ruling this week that backed the Obama administration's campaign to limit greenhouse-gas emissions, a senior Environmental Protection Agency official on Friday said the agency will continue to focus on the largest sources of the emissions in future efforts to curb them.

Gina McCarthy, head of the agency's air-quality office, faced questions from Republicans Friday about whether the agency would use its authority to limit greenhouse-gas emissions to require permits for bakeries, farms, lawnmowers or other relatively small sources.

The EPA can technically impose pollution limits on those small sources under the Clean Air Act, a 1970 law designed to curb air pollution, but it hasn't shown any inclination to do so.

"You're saying you're not going to regulate [small sources] now, but we don't know what you're doing in the future," Rep. Cory Gardner (R., Colo.) told Ms. McCarthy at a House Energy and Commerce Committee hearing Friday.

"It's very clear the direction of this agency," Ms. McCarthy responded. "We are going after the largest sources of greenhouse-gas emissions."

On Tuesday, the U.S. Court of Appeals in Washington upheld the EPA's finding that greenhouse gases linked to climate change endanger public health and dismissed challenges to several regulations that would curb those emissions.

Under the Obama administration, the EPA has proposed greenhouse-gas rules for new coal-fired power plants and taken steps to limit emissions from automobiles. Ms. McCarthy said Friday that limits on greenhouse-gas pollution from refineries, another significant source, aren't imminent.

"We are in discussions on refiners but we are quite a ways away," she said.

Ms. McCarthy also said the agency doesn't have plans to add new greenhouse-gas-permitting requirements to oil and natural-gas wells.

In April, the EPA put in place rules that limit smog-forming chemicals and other toxic emissions from oil and gas wells that use the drilling technique known as hydraulic fracturing, or fracking. Pollution controls installed under those rules are also expected to limit emissions of methane, a greenhouse gas linked to climate change.

Ms. McCarthy said the agency expected those air-quality rules to be sufficient. "At this point the agency has no plans to do more on oil and gas," she said.

Write to Ryan Tracy at ryan.tracy@dowjones.com.