Environmentalists said they were dismayed at some of the report’s conclusions and disputed its objectivity, but they also said it offered Mr. Obama reasons to reject the pipeline. They said they planned to intensify efforts to try to influence Mr. Kerry’s decision. For more than two years, environmentalists have protested the project and been arrested in demonstrations against it around the country. But many Republicans and oil industry executives, who support the pipeline because they say it creates jobs and increases supplies from a friendly source of oil, embraced the findings.

The State Department is expected to shortly release the results of an inspector general’s investigation into the preparation of an earlier draft of the environmental impact report. The investigation was ordered after an environmental group obtained documents indicating that some consultants for the firm that wrote the draft report had previously done work for TransCanada, the company seeking to build the pipeline. If investigators determine a conflict of interest in the preparation of that draft, the State Department may have to conduct a new environmental review.

In light of the investigation, environmentalists were particularly critical of the report released on Friday.

“In what could be perceived as eagerness to please the oil industry and Canadian government, the State Department is issuing this report amidst an ongoing investigation into conflicts of interest, and lying, by its contractor,” said Erich Pica, the president of Friends of the Earth.

Some environmentalists saw reason for optimism in the review, which models several possible future oil market possibilities. Most involve a future of high oil prices and robust demand, in which the oil sands crude is rapidly developed with or without the Keystone pipeline. However, the report offers one alternative sequence, in which oil prices and demand are low. In that case, not building the pipeline might slow development, and thus slow carbon emissions. That possibility is unlikely, but it could provide the administration something to point to should it deny the project.