The European Union has drawn up plans to classify some nuclear power and natural gas plants as green investments that can help Europe cut planet-warming emissions, a landmark proposal that, if approved, could set off a resurgence of nuclear energy on the continent in the coming decades.

The European Commission said it had begun consultations with European Union countries on the proposal, which is intended to provide a common set of definitions of what constitutes a “sustainable investment” in Europe. Any final plan would be subject to approval by a majority of member states, or by the European Parliament.

“The Commission considers there is a role for natural gas and nuclear as a means to facilitate the transition towards a predominantly renewable-based future,” the statement, released on Saturday, said.

The proposal caps one of the most heated political battles in Europe at a time when its leaders have pledged to pull the planet back from the brink of climate catastrophe. It follows months of intense lobbying pitting a pronuclear bloc led by President Emmanuel Macron of France, Europe’s biggest atomic power producer, over objections from Germany and other countries that are wary of a proliferation of nuclear power on European soil.

draft legal text circulated in Brussels over the weekend seeks to strike a middle ground. The proposal would deem natural gas and nuclear power as “transitional” green energy sources to be used to bridge countries’ moves away from coal and carbon-emitting power toward clean energy technologies like wind and solar.

Nuclear power would be considered a sustainable investment if countries can safely dispose of radioactive waste — one of the biggest concerns for the German-led bloc. New plants would be considered sustainable investments through 2045 and would have to undergo safety upgrades during their lifetime to ensure “the highest achievable safety standards,” according to the draft.

Natural gas plants would be deemed “transitional” green energy sources for investment purposes if they meet certain emissions criteria and replace more polluting fossil fuel plants.

The European Union has been working to make sustainability and climate considerations an integral part of its financial rules in order to support the so-called Green Deal, which aims to make Europe a net-zero emitter of greenhouse gases by 2050.

The rules are intended to drive private capital and public money to renewable investments and prevent “greenwashing,” when companies make irresponsible claims of helping clean the environment.

Supporters say natural gas and nuclear can provide critical sources of electricity as economies transition toward cleaner sources like wind and solar, and new technologies like hydrogen power.

But others say neither deserves to be considered a green investment, pointing to carbon dioxide emissions from burning natural gas and the environmental hazards of nuclear plants.

The commission’s proposal is expected to face opposition from members of the European Parliament. Bas Eickhout, a Green lawmaker from the Netherlands, said that classifying natural gas as a green investment would mean “the entire climate leadership of the European Union is down the drain.”

Mr. Eickhout added: “It would also send the wrong signal to the world. If Europe starts calling an investment in gas green, then what exactly is the reason for the African Union not to go fully into gas as well?”

He said the debate has become “a proxy fight” among national leaders for the future of energy in the bloc.

Of the two technologies, however, nuclear power has arguably been the most politically fraught issue.

France led a coalition this year that included nations in Eastern Europe — the continent’s most coal-dependent region — to get nuclear energy and natural gas classified as sustainable investments. Poland, Hungary, Bulgaria and Romania are among the countries that want to attract more investment for nuclear power as they move away from fossil fuels.