As the State Department moves closer to deciding whether to issue a cross-border permit for the Keystone XL pipeline from Canada’s oil sands, the chief executive of the Calgary-based pipeline company appealed Thursday for the U.S. government to balance environmental concerns with economic interests.

During a visit to Washington, TransCanada chief executive Russ Girling also said that his company was exploring other routes to get the Canadian oil to world markets, including a possible retrofit of a natural gas pipeline to eastern Canada that is no longer needed because of the increase in gas produced in the Marcellus shale in Pennsylvania.

“The rhetoric has reached a shrill level and is probably going to get more shrill before a decision,” Girling said in an interview, “and my objective is to dissipate that and get to a rational decision.”

He said that U.S. environmental groups “seemed to coalesce around our project with the narrative that if you shut down the pipeline, you shut down the fuse to the largest carbon bomb on Earth. That just isn’t correct.”

The proposed 1,700-mile pipeline has become the focus of debate because it would link Canada’s oil sands to refineries on the Texas Gulf Coast. Environmental groups and some leading climatologists say that the energy-intensive process of extracting oil from the sands releases greater greenhouse gas emissions than the process for conventional crude oil. Foes of the pipeline say that blocking it would slow development of the oil sands. Activists have staged protests, including a sit-in on platforms hoisted up in trees along the pipeline route in East Texas.

The proposed Keystone XL extension. (Laris Karklis/The Washington Post/Sources: Transcanada, State Department)

Girling said that blocking the pipeline would be a “pyrrhic victory” and that the oil from the oil sands region would find its way to U.S. or other markets where it’s needed.

“You still need the oil. The only question in my mind is: Do you get that oil from Canada, or do you get it from somewhere else?” Girling said. “The crude oil from the oil sands is the same as Venezuelan crude. Barrel for barrel, that’s what we’re going to replace. So denying the Keystone XL pipeline isn’t a win for anybody.”

Girling said construction is 45 percent complete on the southern leg of the pipeline, which last year received permits from the Army Corps of Engineers. The southern leg will run from Cushing, Okla., a major pipeline and storage hub, to a town just north of Port Arthur, Tex.

Much of the pipeline is also complete in Canada, including major river crossings, Girling said. And the steel pipe and pumps needed for the segment running from the Canada-Montana border to Steele City, Neb., are in warehouses ready for installation.

He said that if the Keystone permit is denied, TransCanada would use the steel pipe in other projects.

“In a $50 billion company, it’s not a breaker,” Girling said. “It will hurt — no question about that. But I don’t think that’s a logical answer at the end of the day.”

Lanny Pendill, an oil analyst at the investment firm Edward Jones, said the size of the project is “meaningful” for TransCanada. “Even if unexpectedly this pipeline were not built in the next five-year time frame, they have a good backlog of commercially secured projects. If it doesn’t get approved, it is going to be a negative shock to the stock in the short term,” Pendill said. In the long term, however, “they have the ability to grow the company and the dividend.”

Girling said TransCanada had done work to determine the technical and economic feasibility of converting a natural gas pipeline to an oil pipeline that could carry 850,000 barrels a day of oil from western to eastern Canada. “Our discussions to date, given market differentials, have been very encouraging,” he said.

Refiners in eastern Canada have relied largely on oil imports from west Africa and the Middle East and are paying prices pegged to the London price of Brent quality crude oil, selling for $116 a barrel.

Pendill said prices for Canadian oil are much lower because of transportation bottlenecks, with deep discounts of 20 percent or more below the cheaper benchmark West Texas Intermediate crude, selling for about $97 a barrel.

“So the Canadian producers are pursuing everything possible to access world markets,” Pendill said.

Moreover, Girling said, it is possible to build and retrofit a pipeline to a refinery in Montreal or to the Canadian East Coast city of Saint John, New Brunswick, which has the port capacity to ship about 300,000 barrels a day by tanker to the Texas Gulf Coast. No U.S. permit would be required.

He said oil companies could also choose to ship crude oil from Alberta to the United States by rail, as is now done.