(Adds company comments, updates with LNG details)

By Allison Lampert

MONTREAL, Jan 26 (Reuters) - Canadian Prime Minister Justin Trudeau pledged on Tuesday to require that environmental reviews of oil pipelines and LNG export projects consider greenhouse gas effects, and said it was not his role to be a cheerleader for such projects.

The Liberal government said the new rules would be rolled out within days, and that they would take into account not just the greenhouse gas emissions from a proposed pipeline or liquefied natural gas terminal but also its "upstream" effects, meaning the impact of oil and gas production.

Trudeau did not make clear how much weight would be applied to the emissions. U.S. President Barack Obama rejected TransCanada Corp's Keystone XL pipeline from Canada last year, citing the effect it could have on climate change.

"The federal role is to put into place a process by which TransCanada and any other company could demonstrate that their projects are in the public interest and could have public support," Trudeau told reporters after meeting Montreal Mayor Denis Coderre, who opposes TransCanada's Energy East pipeline.

Energy East would carry 1.1 million barrels of crude oil from Alberta and Saskatchewan across numerous provinces to refineries and export terminals in eastern Canada.

"What we are going to roll out very soon, as we promised in our election campaign, is to establish a clear process which will consider all the greenhouse gas emissions tied to a project, which will build on the work already done."

The Liberals have pledged to strengthen Canada's environmental process and have been working on a transition plan for projects currently under review to ensure they adhere to a higher standard without having to return to square one.

The new rules would apply to major pipeline and LNG projects like TransCanada's Energy East, Kinder Morgan's Trans Mountain expansion and the Petronas-led Pacific NorthWest LNG export terminal.

Projects with existing environmental certificates and pipelines regulated on a provincial level would not be impacted.

Ali Hounsell, spokeswoman for the $5.4 billion Trans Mountain project, said it was too soon to comment on the impact of the new rules but added the company would be eyeing changes to timing.

"When you look at additional process, the key issue for us is timeline," she said. "A small delay in timeline can result in a longer delay on the other end."

TransCanada said it is prepared to work with government to ensure the "safe and environmentally sound" transport of resources to market.

Trudeau has promised the new process would give the various levels of government, scientists and indigenous people the opportunity to take part in decision-making.

(Additional reporting by Julie Gordon in Vancouver, Randall Palmer and Leah Schnurr in Ottawa; Editing by Meredith Mazzilli and James Dalgleish)