The District Department of Human Resources is expanding its program of screening for lead poisoning to include preschool children in all areas of the city, DHR officials said yesterday.

The announcement was accompanied by the release of conflicting information about yet another study of blood-lead levels of children in affluent Ward 3 in upper Northwest.

After denying for almost a year that there is a lead problem in that secor of the city, DHR officials announced yesterday that 8 percent of a group of children tested late this summer had slighty elevated blood-lead levels.

However, while 15 children had elevated levels of the metal in their blood when one testing method was used, a second, more accurate test, found only one child with a blood-lead level considered elevated by the federal Center for Disease Control in Atlanta.

This round of DHR testing was undertaken because of criticism of similar testing last fall, which found that 20 students among 650 tested in Ward 3 had elevated blood-lead levels.

The criticism was based on the fact that the amount of lead in the blood is known to vary with the season, and the testing was done in November, when lower levels usually are found.

The testing done last year was designed to quiet fears raised when Bailus Walker, chief of environmental health for the city, tested a large group of Ward 3 children and found 42 percent with elevated blood-lead levels.

Walker's work was criticized because he refused to say whether a CDC-approved lab had done the blood analysis. He also would not release any data about the children being tested.

Last summer DHR began an attempt to retest children in Ward 3 in response to the criticism that last year's testing had been done at the wrong time of year.

However, all that officials did was send a single letter to each of the parents whose children had been tested the previous November.

The whole question of whether there is a lead problem in upper Northwest Washingtion is highly controversial because the District's lead-screening program, like those in most other jurisdictions across the country, has been aimed at poor neighborhoods with bad housing conditions on the premise that children who have elevated blood-lead levels get them from eating chips of lead-based paint peeling from walls and cellings.

The Walker study said that those children in Ward 3 with elevated lead levels did not live in housing with lead-based paint, leading to the assumption that the lead is in the environment, and that all children thus are vulnerable.

High levels of the metal in the blood can cause brain damage and death.

A recent Boston study, however, found a significant difference in IQ between two groups of otherwise matched children, one group having slightly elevated blood-lead levels, like those children in Ward 3, and one group having only traces of blood lead.