Lead poisoning, previously thought to be a childhood "disease" of poor, innercity neighborhoods, is a serious threat to children living in affluent neighborhoods of Northwest Washington, according to a recently completed study conducted by the District government and Howard University.

Forty-two per cent of the 500 young children studied, all of whom live in such neighborhoold as Cleveland Park. Glover Park. Burleith and Georgetown, had levels of lead in their blood above that considered safe by the federal Center for Disease Control in Atlanta.

None of the children tested between 1974 and 1975 exhibited any of the outward signs of lead poisoning according to the study prepared by Dr. Bailus Walker Jr. director of the Districts Department of Enviromental Services and an adjunct professor of medicine at Howard University Medical School.

However, 55 percent of the 300 1 and 2-year-old tested had between 40 and 59 micrograms of lead per 100 milliliters of blood. The CDC calls 40 micrograms per 100 milliliters the top of the safe scale.

"These children are within what we'd call a scientifically gray zone," said Dr. J. Julian Chisholm, an associate professor of medicine at John's Hopkins University Medical School and one of the nation's leading experts on pediatric lead poisoning.

"You begin to get (changes in the composition of the blood) between 25 and 30 micrograms per 100 milliliters," he said. "When it comes to whether that will cause neurological damage, that's still a hotly debated topic . . . These are undersirable levels," he said, when told of the study's findings.

One of the most disturbing things about the new study is that there is no clear indication of what is causing the high lead blood levels in the affected children.

While children living in dilapidated housing are most often poisoned by eating lead paint chips, and plaster and putty containing lead, none of the homes - all them appraised at $50,000 or above - in which the tested children lived had any tooth marks on the woodwork of peeling paint or plaster.

According to the study, only 5 per cent of the homes had paint with "lead content greater than or equal to 1 per cent", compared to 53 per cent of the homes of inner city children with lead posioning.

The amount of lead in the dust in the more affluent homes, however, "was higher than in the so-called lead belt homes. A similar pattern was also recorded for classrooms." Children with blood lead levels exceeding to micrograms per 100 milliliters lived on homes with five times as much lead in the dust as children with lower lead blood levels, according to the study.

Lead poisoning is an insidious condition that, at its lower and less easily detected levels, can interfer with the blood's ability to metabolize iron and cause anemia.

In more severe cases the lead in the system can lead to severe brian damage, coma and death by causing leakage in the blood vessels of the brian, swelling and pressure within the skull.

Long before they become that ill, however, children fee abdominal pain, loss of appetite, vomiting, drowsiness, irritability and weakness.

Dr. Frederick Green, director of the office of Child Healt Advocacy at Children's Hospital Medical Center, said he is "particularly unhappy to learn of any group of children under the age of 5 who have such a high group under (age) 2, because here we level of lead, and particularly that are dealing with infants and the central nervous system (is still developing) and susceptible to damage.

"I have to assume that any child who has a level of above 40 and is in that preschool, developmental age, is at considerable risk. I am unhappy with a blood level of 30 micrograms," said Green. "There are subtle essential nervous system changes and damage that may occur even with subtoxic levels, even minimal brian damage and subtle learning disorders.

"This constant low level inhalation or injection of lead does build up", in the body, Dr. Green continued. "The body can only excrete a fixed amount a day, something like 50 micrograms a day. So if you inhale 100 micrograms, 50 of that will build up" in the body.

The study found, as have earlier studies in other cities, that children whose homes are closer to roadways, have higher blood-lead levels. One hundred and seven of 119 children who lived less than 100 feet from a road had levels between 40 and 59 micrograms per 100 millititers, while only one of 186 children who lived more than 200 feet from a road had a blood level above 40.

While that would seem to pinpoint automobiles as a primary source of lead contamination, it leaves unanswered such questions as whether the autos themselves are emitting the lead, or whether they are perhaps stirring up lead in the environment or are vibrating homes to such a degree that more lead dust is stirred into the air.

"It's difficult to tell whether the leady you're getting is all the soil or whether it comes from powdering paint", said Chisholm, the co-author in 1956 of one of the first major studies of "The Exposure of Children to Lend."

Many high quality lead paints were designed to powder, said Chisholm, rather than flake. It therefore becomes difficult to tell whether the affected children are bringing leadbearing dust into the house, or are breathing powdering paint in the house.

Both Chisholm and Green expressed concern that the so-called urban pioneering movement, and interest on the part of affluent young couples in rehabiliating older housing, will place their children at risk of lead poisoning.

"Children should be kept out as the housing is being rehabilitated," said Green. "The children should not be in the house when the walls are being abated and remodeled and it should be thorougly cleaned out before the children" move in.

"If the family is living in the house and doing it piecemeal, I think a precaution of keeping a door closed and seeing that the child is not playing in the direct area that is being rehabilitated" is a good idea, he said. "Ideally it's best to have the child live with grandmother or somebody, but if that can't be done then at least the child should be kept out of the area."

Chisholm said he found the District findings a bit surprising "because some of the animal findings have indicated that a good diet", which the children studied presumably have, retards the absorption of lead by the body.

Green and Walker both said that the study points up the need to screen all children in the District for lead poisoning, rather than just poor children. However, said Walker, "I'm not sure the city has the money to go that far."