The ruling by Judge Brian Morris of the United States District Court for Montana repudiates one of Donald J. Trump’s first acts as president. Two days after taking office, Mr. Trump signed an executive order approving the Keystone pipeline that had been blocked by former President Barack Obama because of environmental concerns.

In saying that no work can go forward until the government more fully reviews the pipeline’s environmental impact, the ruling tees up another potentially contentious legal battle over climate change with a president who dismisses mainstream science and whose administration is also seeking to block a landmark lawsuit on behalf of children asking the government to stop the rise of planet-warming gases.