President Obama on Tuesday will call for unprecedented U.S. regulations to reduce carbon emissions from current power plants and a doubling of renewable energy production on public lands, unveiling a blueprint to fight climate change that completely sidesteps Congress and is certain to stoke a broader political fight that will define his second term.

The carbon limits on new and existing power plants are the centerpieces of Obama’s environmental plan, to be announced in a major speech at Georgetown University Tuesday afternoon. A senior administration official said the president would call for his Environmental Protection Agency to develop emissions standards for power plants by June 2014, with the intent of finalizing the plan in June 2015.

It’s an ambitious benchmark full of uncertainty, as the cap on carbon emissions from existing power plants is expected to trigger a flurry of lawsuits both within the electricity industry and from localities that say the regulations would destroy jobs. There’s no guarantee that such measures would even be implemented by the time Obama leaves office.

Obama has faced mounting pressure from liberals to act on climate change after largely ignoring the issue in his first term and pledging to dramatically reduce U.S. greenhouse gases in his State of the Union and Inaugural addresses.

According to the administration official, Obama will not outline specific emission targets on Tuesday, instead tasking the EPA to work with state, local and industry officials to craft limits.

At the same time, the president will call for $8 billion in new loan guarantees for green-energy production and enough renewable projects on public lands to power more than six million homes by 2020.

And Obama will press for stricter efficiency standards for appliances like refrigerators and lamps.

Republican lawmakers are already slamming the blueprint ahead of its release, accusing the president of executive overreach and ramming through a job-crippling green agenda. House Speaker John Boehner, R-Ohio, last week dismissed Obama’s ideas as “absolutely crazy.”

Without congressional support, Obama will frame his go-it-alone approach as one of necessity. However, his environmental policies, at least to date, have not matched his lofty rhetoric on the issue.

The White House points to tens of billions of dollars in stimulus funding for green projects and tighter fuel-economy standards for vehicles as proof of the president’s commitment to tackling climate change. Yet, when a cap on carbon emissions died on Capitol Hill, the president — facing a tough re-election battle — didn’t fight for it.

And missing from Obama’s speech at Georgetown will be any mention of the Keystone XL Pipeline, which could carry oil from Canada to Gulf Coast refineries. Environmentalists are demanding that Obama block the project, under review by the State Department, but the president still won’t telegraph his final decision.

“The bottom line,” a senior administration official said, “is that this proposal is not yet ready for a decision.”