WASHINGTON - The Obama administration is proposing a new rule to tighten restrictions on pollution from coal-burning power plants in the eastern half of the country, a key step to cut emissions that cause smog.

The Environmental Protection Agency said Tuesday the new rule was its most consequential effort yet to tackle deadly pollution that contributes to smog and soot that hangs over more than half the country. The rule would cost nearly $3 billion a year and those costs are likely to be passed along to consumers.

The rule, to be completed in 2011, aims to cut sulfur dioxide emissions by 71 percent from 2005 levels by 2014 and nitrogen oxide emissions by 52 percent in the same period.Known as the Clean Air Interstate Rule, it requires 31 states from Massachusetts to Texas to reduce emissions that can travel long distances.

The rule would overturn and toughen rules issued during the administration of President George W. Bush. While environmental groups and some Democratic lawmakers hailed the new regulation, they conceded that the measure is open to lawsuits that could cause delays in meeting public health targets.

With a comprehensive energy bill facing united GOP opposition in the Senate, Democrats are considering an approach that would focus on capping greenhouse gas emissions from power plants. Some White House officials have begun to speak favorably about such a "utility-only" bill.

A federal judge threw out the Bush clean-air rule in 2008, but an appeals court later reinstated it, while ordering the EPA to make changes that better explain how the rule protects public health.

More than a dozen states sued the EPA, contending that the Bush administration ignored its own experts when it decided in 2006 not to lower the nearly decade-old soot standard.

EPA Administrator Lisa Jackson said the rule signed Tuesday should improve air quality and public health in many states, from southern New England down to Florida, over to Texas and up to Minnesota. The rule does not affect four New England states: Rhode Island, Vermont, New Hampshire and Maine.