Senator Elizabeth Warren of Massachusetts unveiled a public lands proposal on Monday, thrusting land-use issues and the environment into the spotlight as she continues to set the pace on policy in a crowded field of Democratic presidential candidates.

Ms. Warren’s plan, which she outlined in a post on Medium ahead of trips to Colorado and Utah this week, promises an executive order that would prohibit new leases for fossil fuel drilling offshore and on public lands, calls for the creation of “a 21st century Civilian Conservation Corps” staffed by 10,000 young people and seeks to reduce inaccessible public acreage by 50 percent.

It also aims to undo some of the environmental actions undertaken by the Trump administration, which she said amounted to “selling off our public lands to the oil, gas and coal industries for pennies on the dollar,” accelerating a “climate crisis” in the process. Under the plan, Ms. Warren said she would reinstate Obama-era air and water protections and wield the Antiquities Act, a 1906 law, to restore national monuments that President Trump shrank.

“America’s public lands are one of our greatest treasures,” she wrote in the Medium post. “But today, those lands are under threat.”