The Bush administration outlined its five-year strategy Thursday to combat toxic lead, with federal health officials calling lead poisoning the No. 1 environmental hazard facing U.S. children.

The plan, to be unveiled at a Senate hearing, calls for the Department of Health and Human Services to conduct nationwide lead screening of children, for the Department of Housing and Urban Development to test ways to clean lead paint out of older homes and for the Environmental Protection Agency to tighten regulations on the amount of lead released into the environment.Lead is a metal found most commonly in lead-based paint, soil and dust and drinking water that can have a variety of adverse effects on human health, especially in children, including damage to the reproductive and neurological systems.

As many as 17 percent of U.S. children under age 6 - about 3 million to 4 million youngsters - may have levels of lead in their blood high enough to cause mental and behavioral problems and other adverse health effects, officials said.

"Lead poisoning is entirely preventable, yet it is the most common and societally devastating environmental disease of young children," said HHS Secretary Louis Sullivan.

"Many people think lead poisoning is a thing of the past. Lead paint has been banned, lead gasoline and lead-soldered cans greatly reduced. Our first task is to make sure everyone knows that lead continues, despite great progress, to be very dangerous to young children," he added.

A study released last year showed young people exposed to moderate levels of lead as preschoolers were seven times more likely to drop out of high school, HHS said.