UN Ambassador Susan Rice and her husband are major shareholders in TransCanada, the company that’s trying to build the Keystone XL pipeline. (Evan Vucci/AP)

If Susan E. Rice becomes Secretary of State, she might have to recuse herself from one of the first and most controversial decisions she would face: the Keystone XL oil pipeline permit.

The reason: Rice and her husband are major shareholders in the pipeline company as well as a variety of Canadian companies that are involved in exploiting the oil sands region of Alberta, which would feed the Keystone XL and benefit from a new outlet.

The couple owns $300,000 to $600,000 of stock in TransCanada, the pipeline firm, and they own stakes of more than $1.25 million each in four Canadian companies — Imperial, Encana, Enbridge and Cenovus — that have been active in the oil sands region of northern Alberta. Enbridge is also the company whose pipeline ruptured and spilled crude into the Kalamazoo River in Michigan last year.

Rice and her husband also own shares of major Canadian banks that are expected to provide financing for the Keystone XL project. They own between $50,000 and $100,000 of shares in Suncor, another oil sands company, and more than $1.25 million of shares in Transalta, the Alberta’s electric power producer.

Rice, who is the U.S. ambassador to the United Nations and considered the leading candidate to become President Obama’s nominee for State, listed the holdings in her most recent disclosure statement, covering the 2011 calendar year. The information was highlighted in an article published on the Web site of the Natural Resources Defense Council’s OnEarth magazine. The NRDC is opposed to the construction of the $7 billion pipeline.

“We oppose the Keystone XL,” said NRDC associate director of communications Bob Deans. “It would send some of the dirtiest oil on the planet through the breadbasket of America to be shipped overseas from the Gulf of Mexico. It’s not in our national interest: it’s a profit scheme for big oil.”

There is nothing inappropriate about the investments, and Rice’s connections to Canada go back 20 years, when she was working in the Toronto office of the McKinsey & Co. consulting firm and her husband, Ian Cameron, was a television producer there for the Canadian Broadcasting Co. Cameron, who like Rice graduated from Stanford University, is from Canada.

Rice and Cameron are well off. They were worth between $23.5 million and $43.5 million in 2009, according to the Center for Responsive Politics. (Those figures were also highlighted on the OnEarth Web site.)

In a statement, Rice’s spokeswoman, Erin Pelton said “Ambassador Rice is in full compliance with all financial disclosure requirements related to her service in the U.S. government and is committed to continuing to meet these obligations.”

Rice has not been nominated for the position of Secretary of State, although Obama has defended her qualifications for the job. If she did become secretary of state, Rice could also sell the shares or put them into a blind trust and try to retain her authority to issue or deny the pipeline permit.

At a time when Obama is fighting Republicans opposed to Rice, the financial disclosure form is likely to draw scrutiny from Democrats and environmental activists who have been among the president’s most reliable supporters.

TransCanada originally proposed the 1,700-mile Keystone XL pipeline to take oil sands crude from Alberta to Texas, where many refineries have the ability to refine the low-quality Canadian crude. The pipeline needs the approval of the State Department because it crosses an international border.

But the pipeline proposal aroused criticism from U.S. environmentalists, who said that the process of extracting crude from oil sands was energy intensive and therefore emitted more greenhouse gases than conventional oil production. The thick oil sands are tapped either in strip mines or through an injected steam process.

Opposition also sprouted in Nebraska, where residents feared that a possible leak might contaminate rivers or water supplies, including portions of the ecologically sensitive Ogallala aquifer, which provides irrigation water to farmers and ranchers in eight states.

Republicans tried to force Obama to approve the pipeline early this year by setting a deadline in legislation extending the Social Security tax cut, but Obama rejected the pipeline proposal instead, saying that the State Department needed more time to consider the project.

The move also delayed a sensitive topic until after the presidential election.

Obama then embraced the southern leg of the pipeline, starting in Cushing, Okla., a major oil pipeline terminal. That portion of the project has received approval from the Army Corps of Engineers and is under construction, despite a determined group of protestors engaged in civil disobedience in northeast Texas.

The northern leg of the project, which would run from the Canadian border in Montana to Steele City, Neb., still requires approval.

Environmental groups are also sensitive because of earlier controversies over whether State had kept a proper distance from TransCanada and whether its Environmental Impact Statement took into account the emission of greenhouse gases from oil sands mining.

When Obama rejected the Keystone XL pipeline, he said the State Department would consider a new permit application, which TransCanada has filed, amended to circumvent the most sensitive areas of Nebraska.

If all goes as planned, the State Department is expected to make a decision sometime in the first quarter of next year.

Sen. John F. Kerry (D-Mass.), another potential secretary of state for Obama, and his wife, Teresa Heinz Kerry, have a net worth of $181 million to $282 million, according to his most recent disclosure statements. Kerry’s wife was previously married to the late senator H. John Heinz III (R-Pa.), who died in 1991. The Kerrys’ more diverse set of investments includes $250,000 to $500,000 of shares in Suncor, held in a Heinz family stock fund.

Anne Gearan contributed to this report.