In a stunning improvement in children's health, far fewer kids have high lead levels than 20 years ago, new government research reports - a testament to aggressive efforts to get lead out of paint, water and soil.

Lead can interfere with the developing nervous system and cause permanent problems with learning, memory and behavior. Children in poor neighborhoods have generally been more at risk because they tend to live in older housing and in industrial areas.

Federal researchers found that just 1.4 percent of young children had elevated lead levels in their blood in 2004, the latest data available. That compares with almost 9 percent in 1988.

"It has been a remarkable decline," said study co-author Mary Jean Brown of the Centers for Disease Control and Prevention. "It's a public health success story."

The 84 percent drop extends a trend that began in the 1970s when efforts began to remove lead from gasoline. The researchers credited continuing steps to reduce children's exposure to lead in old house paint, soil, water and other sources.

The study was being released Monday in the March edition of the journal Pediatrics. It is based on nearly 5,000 children, ages 1 to 5, who were part of a periodic government health survey.

The government considers levels of at least 10 micrograms of lead per deciliter of blood to be elevated, although research has shown that levels less than that can still cause problems including attention and reading difficulties. There is no known "safe" level, the study authors noted.

Caroline Cox, research director of the Center for Environmental Health, a California-based advocacy group, noted that lead poisoning "is entirely preventable."

"There's no reason even one child in the United States should be poisoned by lead," Cox said. "It's great there aren't as many now as there were, but there are still too many."

By 2004, racial disparities among children with blood-lead levels higher than 10 micrograms had mostly disappeared: About equal numbers of white, black and Mexican-American children had levels in that range.

However, disparities at lower levels remained. For example, almost 18 percent of white children had levels of less than 1 microgram per deciliter, versus 11 percent of Mexican-Americans and 4 percent of blacks.

Children from lower-income families also had higher lead levels than those from wealthier families.

Dr. Bruce Lanphear, a lead specialist at Cincinnati Children's Hospital Medical Center who wasn't involved in the government study, said lead levels have probably continued to decline since 2004. But the findings show "we need to still continue to be aggressive" with prevention efforts, he said.

Lead-based paint in old housing, which can contaminate house dust and soil, is the main source. Children also can be exposed to lead in water, mostly from old plumbing pipes, as well as toys and certain folk medicines.

The CDC recommends that pregnant women and young children avoid housing built before 1978 that is undergoing renovation. Other recommendations include regularly washing children's hands and toys; frequent washing of floors and window sills, where paint dust can collect; and avoiding hot tap water for drinking, cooking and making baby formula. Hot tap water generally contains higher lead levels from plumbing than cold water.