Nothing prepared Veronica Rodriguez** for the call she got from a New York City health official last October.

A blood sample taken from her 2 1/2-year-old son, Carlos Espinoza, had revealed more than double the level of lead that the federal government considers cause for concern about poisoning.

"I was horrified," said Ms. Rodriguez, 26, who lives on Staten Island and vaguely recalls having heard routine prevention messages about the dangers of lead in the home. "I thought, oh my God, my boy is very sick."

Lead poisoning among young children, which can cause learning and behavior problems, has decreased so sharply in recent decades that it is tempting to consider it a problem of the past. The Centers for Disease Control and Prevention was so confident about the decline in childhood lead poisoning that it set a goal of 2010 for eliminating it.

But federal health officials now say eradication may still be years away because hazards remain in often poor urban pockets — mostly from old, badly maintained housing with lead-based paint.

If the remaining cases are to be tackled effectively, local laws must be strengthened and enforcement increased, experts say.

"We have to get serious about doing these things," said Dr. Mary Jean Brown, chief of the lead poisoning prevention branch at the C.D.C.

Many jurisdictions still do not have lead hazard laws, which require landlords to check for exposed lead-based paint if children are living in the home, Dr. Brown said. And even in New York City, which passed a comprehensive law in 2004, compliance is spotty.

A survey of 120 tenants in Bushwick, Brooklyn — among the neighborhoods with high lead levels in children — found "rampant noncompliance" among landlords from 2007 to 2009. In the survey, by the community groups Make the Road New York and the New York City Coalition to End Lead Poisoning, 59 percent of tenants reported that their landlords had not followed any of the law’s provisions.

An earlier wave of increased testing and tougher legislation, including bans on lead-based paint in the 1970s and on leaded gasoline in the 1990s, resulted in sharp declines in poisoning cases in the most vulnerable population, children younger than 6. In 2006, an estimated 120,000 children under 6 tested positive for elevated lead levels nationwide, according to the C.D.C., down from 434,000 in 2000 and 890,000 in 1994.

New York City’s rates of lead poisoning mirror the national trend, with 1,572 cases among children tested in 2008, compared with 20,000 in 1995.

After more than two decades of delays, the Environmental Protection Agency will put a regulation in effecton Thursday that requires renovation and remodeling contractors to be certified in techniques for containing lead dust stirred up during work. The rule, which contractors say could increase the cost of renovation projects by hundreds of dollars, applies to homes and buildings housing children that were constructed before lead paint was banned in 1978.

In New York, a task force convened last summer by Gov. David A. Paterson is also exploring ways to incorporate lead inspections into requirements for building permits and state assistance, like money for weatherization projects. The task force is to issue its report in November.

"At this point, it’s really trying to identify opportunities to try to get ahead of the problem," said Wendy Saunders, the state’s deputy secretary for health, Medicaid and oversight, who is vice chairwoman of the task force.

But the invisible threat persists in the city’s so-called lead belts — areas of Brooklyn, Queens and Staten Island where the rates of children showing elevated levels are routinely the highest in the city.

Last summer, E.P.A. officials took hundreds of soil samples near a long-closed lead factory on Staten Island suspected in the chronically higher rates of lead poisoning among children in the North Shore neighborhoods of Port Richmond, Stapleton and St. George. The area was once filled with heavy industry, and lead contamination can be found in parks and industrial sites.

Of the children tested from those neighborhoods, about 7 out of 1,000 had elevated lead levels, health department data show, compared with a citywide average of 4.5 out of 1,000.

But when the soil sampling results came in last month, the lead contamination found in six residential blocks was traced to peeling paint, not the plant. The samples contained an average lead concentration of 549 parts per million, well above the threshold of 400 parts per million that the E.P.A. says is a health risk in residential areas for children.

Walter Mugdan, the E.P.A.’s regional Superfund director, said that the paint had contaminated backyard soil that could also harbor traces of leaded gasoline. The samples, he said, were "very typical" of what would be found in heavy-traffic urban areas.

The lead could pose a risk of poisoning for children if they played in the soil or were otherwise in contact with it, Mr. Mugdan said, and he recommended that property owners cover the soil with mulch, plantings or concrete, and that they paint over any lead-based paint or strip it off carefully to avoid spreading it.

But community advocates on Staten Island want more aggressive government action. They are asking for a federal or city cleanup in residential areas similar to what the E.P.A. plans for the old lead factory site.

"If the problem is so common, why not come up with a model project to address it?" said Beryl A. Thurman, executive director and president of the North Shore Waterfront Conservancy of Staten Island, a watchdog group. "It’s not enough to have the department of health tell people, ‘Make sure you wash your hands and put down some wood chips.’ "

Community advocates and public interest lawyers say an underlying problem is lax enforcement of the city’s 2004 law requiring landlords to conduct annual inspections of homes where children under 6 are living and to correct lead hazards.

Ms. Rodriguez said the $1,300-a-month apartment in Port Richmond that she shared with another family had no peeling paint except behind the heater. But when her son’s test results after a checkup showed a lead level of 25 micrograms per deciliter of blood, it led to an inspection by the city’s Department of Health and Mental Hygiene. The inspector found lead in 23 of 154 readings taken from walls and windowsills, his report said, as well as mold and missing detectors for smoke and carbon monoxide.

A spokesman for the Department of Housing Preservation and Development said that officials were not available to comment for this article but that the agency had issued 31,463 violations in 2009 over complaints about lead paint and did more than $6 million worth of work to correct lead hazards.

Some doctors say that the C.D.C. could act more aggressively to identify poisoning cases by lowering the threshold at which lead levels are considered elevated. That threshold is 10 micrograms per deciliter of blood in children under 6. But Dr. John Rosen, who founded the lead program at Montefiore Medical Center in the Bronx in 1972, said research had established that even at levels as low as 5 micrograms per deciliter, lead could cause irreversible impairment to intelligence quotient, motor skills and behavior.

"The current level is not safe," said Dr. Rosen, whose program cares for 1,200 children and runs a safe house for families who need to flee their homes because of lead contamination.

Since Ms. Rodriguez and her son moved in November, to a cramped second-floor apartment they share with relatives, Carlos’s lead level has fallen to 8.7. On a recent afternoon, he bounded up the stairs after his mother, munched on Cheetos and watched "Thomas and Friends" on television before falling asleep in midmotion on a plastic chair.

Ms. Rodriguez said she was on high alert for any signs of illness in her son and washed his hands several times a day. She was also following doctor’s orders to give him iron supplements and feed him a diet high in dairy products and vegetables.

Watching Carlos sleep, Ms. Rodriguez said she was not as panicked as she had been when she first learned he had lead poisoning.

"I worry about whether he’ll be able to learn like other children," she said, breaking down in tears. "He’s so little. The question is, how will he do in the future?"

**Member of Make the Road New York