ST. PAUL — Minnesota utility regulators are preparing to discuss restarting the approval process for Enbridge Energy’s plan to replace its aging Line 3 crude oil pipeline across northern Minnesota.

The project had been on hold because of legal challenges by environmental and tribal groups that say the upgrade would aggravate climate change and pose an unacceptable risk of spills into sensitive lakes, streams and wetlands.

The Public Utilities Commission meets Tuesday to decide how to proceed in complying with a court order to supplement the project’s environmental review with more analysis of the potential effects of spills in the Lake Superior watershed.

Once that study is completed, the PUC must take public comments before approving it. Then the commission and other agencies would have to reissue some other key approvals and permits.