The EPA plan, promised by new administrator Lisa Jackson during her Senate confirmation hearings in January, calls for regulators to identify 50 to 100 schools where pollution might pose significant health risks. At many of those locations, the agency will work with state and local regulators to monitor the air for a variety of toxic chemicals.

The agency could begin taking air samples within five weeks and may release some results within a few months. The cost of the effort is expected to be about $2.5 million and will be funded "through redirecting resources from the current budget as well as from the next fiscal year," says EPA spokesman Allyn Brooks-LaSure. "This is a priority."

The plan, the agency's first effort to systematically examine industrial pollution outside schools, comes in response to a USA TODAY investigation that used the government's own data to identify schools that might be in toxic hot spots — areas where chemicals may permeate the air.

Children are particularly susceptible to toxic chemicals; they breathe more air in proportion to their weight than do adults, and their bodies are still developing. Exposure to some chemicals can trigger ailments such as asthma or lead to cancer years or even decades later.

The newspaper's investigation, published in December, used a government computer simulation that showed at least 435 schools where the air outside appeared to be more toxic than the air at an Ohio elementary school closed in 2005. There, the Ohio EPA found levels of carcinogens 50 times what the state considered acceptable. USA TODAY subsequently teamed with Johns Hopkins University and the University of Maryland to take "snapshot" air samples near 95 schools in 30 states. At 64 of those locations, the newspaper found elevated levels of chemicals.

In most cases, no one knows for certain what's in the air. That's because the Clean Air Act doesn't require regulators to check for hundreds of the most dangerous chemicals.

The EPA plan comes as two states — Pennsylvania and Louisiana — say their own monitoring showed no problems near schools. Friday, Pennsylvania issued a news release saying its monitoring outside four schools found "no unsafe levels of air pollutants." The agency based its conclusion on about 12 days of monitoring, including some during Christmas week 2008. It did not say whether nearby industries were operating during its monitoring.

Such findings could influence where the U.S. EPA monitors, but Jackson vowed the issue has "the full attention" of the agency. "This is going to remain an urgent matter for us," Jackson said. "I plan to remain personally involved in this." She said getting definitive answers might take months.

During the confirmation hearing in January, Sen. Barbara Boxer, D-Calif., pushed Jackson to commit to monitoring outside schools. In a statement, Boxer said she was "pleased" with the EPA plan.

"Congress was right to be seized by this," Brooks-LaSure said. "We need to move into action."