Many homeless children tested by health workers in the New York City shelter system suffered from iron deficiency and other symptoms of malnutrition that could severely affect their long-term health, according to a survey by an advocacy group for the homeless.

The yearlong study of 200 children was done by the New York Children's Health Project, which operates four medical vans that travel among some of the city's shelters providing free care. The study was not scientifically designed to project precisely the extent of poor nutrition among the city's nearly 10,000 homeless children.But the doctors who worked on it, and other advocates for the homeless, said the findings were a sign that the health of children in the shelter system, already at risk because of their families' economic and social instability, is further imperiled by a poor diet.

They said the problem resulted not only from poverty but from a shelter system that makes it difficult for mothers to feed their children well.

The study found that 42.5 percent of children between ages 1 and 3 living in the shelter system suffered from iron deficiency or anemia - a level twice as high as the national average for children living below the poverty level and six times greater than for those living above it.

Preschool children between 3 and 5 fared even worse. Their rate of anemia and iron deficiency - 24.7 percent - was 2 1/2 times the national average for poor children and 10 times greater than for children in economically stable homes.

Nutritional deficiencies have also been shown to cause problems in children's cognitive development.