WASHINGTON — The short-term plan to reduce greenhouse gas emissions that President Obama outlined this week is achievable with some new programs and better management of existing ones, the new energy secretary, Ernest J. Moniz, said in an interview on Thursday. But he said reaching a longer-term goal would require bigger reductions as well as action from Congress.

When Mr. Obama first ran for president, he pledged to reduce greenhouse gas emissions in the United States 80 percent by 2050, compared with 1990 levels.

Mr. Obama’s interim goal, for 2020, is a 17 percent reduction in global warming gas emissions compared with 2005. The 2020 goal is already half achieved, Dr. Moniz said, and achieving the rest will require faster fulfillment of new appliance efficiency standards, among other steps. Many of those standards are stuck in a bottleneck at the Office of Management and Budget, which evaluates the costs and benefits of proposed regulations.

“I think the president’s commitment will provide the spur to O.M.B. and the Energy Department to move smartly on these,” Dr. Moniz said.

Other steps include government loan guarantees for fossil fuel projects that will cut pollution, which the Energy Department will administer but has yet to describe in detail.

“Fossil fuels are not going away any time soon,” Dr. Moniz said. He said it was essential to build power plants that would capture and bury their carbon dioxide emissions and that after that technology was commercialized for coal it would have to be used on natural gas as well. Carbon emissions from power plants that use natural gas are about half of those from coal, but they are still not nearly small enough to meet long-term climate goals, he said.

Another step, he said, is the completion of new civilian nuclear power reactors at a price and on a schedule close to what has been budgeted. The department is still negotiating a loan guarantee for one of those projects, Vogtle 3 and 4, near Waynesboro, Ga. He said that the four new reactors under construction — the other two are in South Carolina — were only slightly larger, in capacity, than the four reactors whose retirements have been announced this year. In the long term, he said, it was essential that the plants under construction become templates for building more.

By midcentury, when the president’s goal is an 80 percent reduction in emissions compared with 1990, “you have to replace essentially all the nuclear capacity, and build more,” he said.

Production of a new kind of factory-built “small modular reactors“ would also be needed, but those would not be deployed by 2020, he said.

One of the big steps the president described this week was setting standards for carbon dioxide emissions from power plants. The Energy Department might play a role in helping improve power plant efficiency, but the standards would be set by the Environmental Protection Agency.

To reach the 80 percent goal, set forth by Mr. Obama when he first ran for president, would require cutting emissions every year by about 20 percent more than what the president proposed this week, said Daniel M. Kammen, director of the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley. Mr. Kammen also said the 17 percent goal is “not as deep as I would like initially, but it’s critical to do this step.”

Dr. Moniz said that the interim goal was compatible with the long-term goal, but reaching the 2050 goal “would require a lot more to happen.”