CAMBRIDGE, Mass. — PRESIDENT OBAMA is expected to announce his much anticipated rule for power plants on Monday, requiring for the first time that older and dirtier plants reduce their carbon dioxide emissions, which account for a sizable share of the nation’s carbon pollution.

This new rule has rightly been called the “cornerstone” of the president’s climate action plan. If successful, it has the potential to transform the nation’s power sector by driving new investments in efficiency and renewable energy, and by increasing the use of cleaner natural gas in place of coal.

But don’t expect big changes anytime soon. Legal challenges could tie up this effort for years.

This is the sad reality of climate policy in the United States circa 2014. With Congress paralyzed on the issue, the country’s climate and energy policy is being made in arcane legal battles over the meaning of single phrases in statutes written long ago, leaving government and industry to duke it out in court.

The Environmental Protection Agency’s authority to regulate the nation’s approximately 550 existing power plants comes from a little-known section of the Clean Air Act known as 111(d). This section requires states to adopt performance standards for existing sources of pollution. The E.P.A. sets benchmarks that the states must meet and can improve upon.