WASHINGTON - If you've been putting off repairing a peeling windowsill, or you're thinking of knocking out a wall, listen up: Check how old your house is. You may need to take steps to protect your kids from dangerous lead.

The risk of lead-based paint from older homes is back in the news, as the government considers tightening the definition of lead poisoning in babies, toddlers and preschoolers. Lower levels than previously thought may harm their developing brains.

That's a scary-sounding message. But from a practical standpoint, it's not clear how much would change if the government follows that advice. Already there has been a big drop in childhood lead poisoning in the U.S. over the past few decades. Public health programs have targeted the youngsters most at risk - poor children living in crumbling housing, mostly in cities - to try to get them tested and their homes cleaned up.

But specialists say it can be a risk in more affluent areas, too, as do-it-yourselfers embark on fix-ups without knowing anything about an environmental hazard that long ago faded from the headlines.

The main value of the proposed change may be in increasing awareness of how to avoid lead in everyday life.

"What we need to do is prevent the exposure in the first place," said Dr. Nicholas Newman, who directs the environmental health and lead clinic at Cincinnati Children's Hospital.

There are lots of ways people can be exposed to lead: Soil polluted from the leaded gasoline of yesteryear. Old plumbing with lead solder. Improperly using lead-glazed pottery or leaded crystal with food. Certain jobs that expose workers to the metal. Hobbies like refinishing old painted furniture.

Sometimes even imported toys or children's jewelry can have illegal lead levels, prompting recalls if they're caught on the U.S. market.

But the main way that U.S. children are exposed is from layers of old paint in buildings built before 1978, when lead was banned from residential paint.

Sure, the walls might have been painted over recently, and there may be no obvious paint chips to attract a tot crawling around on the floor. But friction from opening and closing windows and doors allows tiny leaded particles to make their way into household dust - and youngsters then get it on their hands that go into their mouths, explained Dr. John Rosen, a lead poisoning specialist at the Children's Hospital at Montefiore in New York City.

Very high lead levels can cause coma, convulsions, even death, fortunately a rarity today. But lower levels, especially in children under 6, can harm a child's brain, can reduce IQ and cause other learning, attention and behavioral problems - without any obvious symptoms to alert the parent.

How much is too much? Until now, the definition of lead poisoning in young children was 10 micrograms of lead per deciliter of blood. But in a draft report last fall, the National Toxicology Program analyzed recent scientific research to conclude there's good evidence that levels lower than 10 are a risk. Now advisers to the Centers for Disease Control and Prevention are urging that agency to lower the definition to 5 micrograms for now, periodically reassessing.

If the CDC agrees, its advisers estimated that could classify about 450,000 children with lead poisoning, up from roughly 250,000 today.

At these levels, there's no treatment for the child other than to end the ongoing exposure - clean up the house, Newman stressed. That's why prevention is so important. And while the youngest children are the most vulnerable, lead's not good for anyone's brain, so he advises taking common-sense precautions before potential exposures like renovating an old home.

What should families do? Here's advice from the Environmental Protection Agency and public health agencies:

• Check the age of your house. At checkups for babies through age 5, pediatricians are supposed to ask if you live in a home built before 1960, or one built before 1978 that's recently undergone renovation. The answers help guide who may need a blood test to check lead levels. Some states require testing of toddlers on Medicaid.

• Wash kids' hands before they eat, good advice no matter where you live or how old your house.

• Clean up paint chips immediately, and regularly wash toys that tots put in their mouths.

• Regularly wash windowsills and floors where paint dust can collect.

• If you're planning repairs or renovation in an old building, use lead-certified contractors who must follow EPA rules to minimize exposure from the work and can perform quality tests to see if your old paint really contains lead.

• If you rent and have peeling paint, notify your landlord. Many cities and states have lead-abatement rules, and programs to contact for help.

• Aside from paint, take off shoes at the door, to minimize tracking in lead-tainted soil.

• Use only cold water for drinking, cooking and making baby formula, and run it for 15 to 30 seconds. Hot tap water can pick up more lead from older plumbing than cold water.