WASHINGTON — The debate within the Trump administration over what to do about the Paris climate agreement has reached a critical phase, according to people familiar with the internal negotiations. The decision could hinge on the interpretation of a single phrase in a single provision of a document that took years to write.

The question is whether to walk away from the agreement sealed by the Obama administration and nearly 200 other nations at the end of 2015 — as Donald J. Trump promised as a presidential candidate to do — or to weaken the nation’s commitment under the deal to reducing greenhouse gases while remaining in the accord.

The provision at issue, Article 4.11, states that a nation “may at any time adjust its existing nationally determined contribution with a view to enhancing its level of ambition.” The question is whether the ability to “adjust” is like a ratchet, allowing progress only in one direction — upward — or if it permits a country to weaken its commitment without violating the terms of the deal.

The fight within the White House over what to do about the Paris deal has been going on for months. One side, led by the president’s chief strategist, Stephen K. Bannon, and Scott Pruitt, the administrator of the Environmental Protection Agency, has argued that the language of the provision does not allow nations to weaken their commitments. They urge the president to withdraw entirely from the Paris deal.