Just days before ConocoPhillips’ Alaska division was slated to begin construction of the long-planned Willow oil project, a federal judge ordered a delay in response to a lawsuit by environmental groups that alleges former President Trump’s administration overlooked wildlife and climate change impacts.

In a decision issued on Saturday, U.S. District Court Judge Sharon Gleason temporarily prevented ConocoPhillips from opening a gravel mine or building a gravel road at the Willow site, which is located within the Bear Tooth Unit of the National Petroleum Reserve in Alaska.

Gleason had early last week denied conservation groups’ requests to block ConocoPhillips from starting construction until after legal challenges were completed. The judge said then that the groups had not...