For the doctor behind a $3 billion national study of children’s health, Philip Landrigan, the idea of identifying environmental triggers for common diseases is a priceless endeavor.

Billed as the largest-ever study of children’s health, the National Children’s Study seeks to follow 100,000 children from conception to age 21. With the goal of identifying some of the environmental causes of diseases such as asthma, diabetes, and cancer, researchers aim to sign up children from 105 counties across the country, and they plan to knock on doors to enroll 2,000 babies or pregnant women from each location in the coming months.

Children will be monitored every other year to measure exposure to pathogens in “real time,” according to Dr. Landrigan, the chairman of the Department of Community and Preventive Medicine at Mount Sinai’s School of Medicine. He helped design the study.

“The whole study is driven by a focus on trying to identify the environmental factors that are responsible for the big diseases affecting children in America today,” Dr. Landrigan said in a recent interview at Mount Sinai, where he sat in a conference room surrounded by two decades’ worth of articles from the journal Environmental Health Perspectives and books with titles such as “Asbestos: Medical and Legal Aspects” and “The Pesticide Conspiracy.”

“We’re going to be able to turn it into a blueprint for disease prevention,” he said.

A graduate of Harvard Medical School, Dr. Landrigan, 66, completed his medical residency at Boston Children’s Hospital, where he first encountered children with lead poisoning. “That was my first realization the environment could influence children’s health,” he said. In 1970, he took a job at the Centers for Disease Control and Prevention, and supervisors dispatched him in 1971 to El Paso, Texas, to investigate possible health effects of lead exposure in children.

In 1985, Dr. Landrigan left the CDC to head up Mount Sinai’s Department of Community and Preventive Medicine, where for the past seven years he has been recognized for his work investigating the health impact of the terrorist attacks of September 11, 2001. Through the Mount Sinai Medical Monitoring and Treatment Program, he and other Mount Sinai doctors tracked about 25,000 workers who responded to the World Trade Center site. “On top of everything it was to all of us, it was also the largest active environmental disaster that happened in New York City,” Dr. Landrigan said.

The native of Boston traced his interest in the environment to his childhood, during which he spent time hiking in a state park, the Blue Hills Reservation in Milton, Mass. The park is about 30 miles northwest of the town of Framingham, the site of a multigenerational heart study starting in 1948 that led researchers to identify the major risk factors for cardiovascular disease.

“All of it has just become what every American now knows about heart disease and stroke,” Dr. Landrigan said. “I’m hopeful that we can do something similar,” he said in describing his goals for the National Children’s Study.

The $3 billion study, authorized by Congress in the Children’s Health Act of 2000, has faced funding obstacles and delays. Three years ago, the Bush administration called for termination of the study. Most recently, researchers were set back several months after an internal review board asked them to make small adjustments to their plans.

“It takes a lot of patience and it takes a lot of persistence,” Dr. Landrigan recently observed. Asked if the next president could change the course of current progress, he responded: “Could they? Sure. Would they? I don’t think so. I think it’s a good thing for America.”

Researchers familiar with the project said they expect that the study will illuminate triggers for chronic diseases, such as asthma. “One of the key questions out there is, ‘How much of the problem is from environmental factors?'” a professor of environmental medicine at New York University’s School of Medicine, George Thurston, said. Between 2001 and 2003, Mr. Thurston, who is a doctor of science, led a study of asthmatic children in the South Bronx, equipping them with backpacks that measured levels of air pollution. The results are to be published shortly.

He said a national study would act as a “guide” to physicians. “The more you understand about the pathogen of disease, the more you can assess it and appropriately treat it,” he said.

In the National Children’s Study, all of the locations were selected using a mathematical formula to ensure children from different backgrounds were represented. Enrollment will kick off in seven “vanguard” centers, including Orange County, Calif.; Duplin County, N.C.; Montgomery County, Pa.; Brookings County, S.D.; Lincoln, Pipestone, and Yellow Medicine counties in Minnesota; Salt Lake County, Utah; Waukesha County, Wis., and Queens County in New York. “No county will be dominant,” Dr. Landrigan said. “They’re quite different.”

Medical doctors in Queens said they expect the borough’s diversity to have a significant impact on the findings. “They did a good job when they chose Queens because they’re going to find a lot of varieties for disease patterns,” an internist who is the immediate past president of the Queens County Medical Society, Dr. Inderpal Chhabra, said. Saying that heart disease was a major concern of his, Dr. Chhabra said the biggest limitation of the Framingham study was a homogenous population. In Queens, he said, researchers would find a “little bit of this, a little bit of that.”

“When you talk about the melting pot, I think that’s what Queens is,” he said.