Which means the pipeline almost certainly won’t be approved.

WASHINGTON — President Barack Obama will ask the State Department not to approve the construction of the controversial Keystone XL pipeline unless it can first determine that it will not lead to a net increase in greenhouse gas emissions, a senior administration official told The Huffington Post.

The policy pronouncement will come during the president’s highly publicized speech on climate change at Georgetown University on Tuesday. It will add another chapter to what has been the most politically difficult energy-related issue confronting this White House.

The president has avoided weighing in on the construction of the Keystone XL pipeline for several years now, citing an executive order asking the State Department to make a determination on the project’s viability first. Environmentalists have called on him to spike the project entirely because of risks that it will contribute irrevocably to global warming and potentially contaminate drinking water if it leaks. Conservatives and even some labor groups have encouraged Obama to approve of the project because of its potential to create jobs.

The new Obama policy somewhat splits the difference — not killing the project outright, but ensuring that it meets a basic environmental standard.

“As the executive order on Keystone contemplates, the environmental impacts will be important criteria used in the determination of whether the Keystone pipeline application will ultimately be approved at the completion of the State Department decision process,” said the senior administration official. “In today‚Äôs speech, the president will make clear that the State Department should approve the pipeline only if it will not lead to a net increase in overall greenhouse gas emissions.”