Nearly one of every five Americans served by public water systems consumes levels of lead in drinking water higher than the government considers safe, according to preliminary findings of the Environmental Protection Agency.

The excess lead found in the drinking water of 38 million people nationwide accounts for slightly lower intelligence among 143,500 children every year, according to a draft copy of a new EPA report. It also accounts for 118,400 cases of hypertension, 75 strokes and 370 heart attacks among middle-aged white males, and higher risk of pregnancy complications among 622,000 women of child-bearing age, according to the EPA analysis.

In financial terms, the lead contamination problem costs more than $ 1 billion a year in medical care, plumbing repairs and specialized education and reduced future earnings among children with learning disabilities, the report said.

The EPA report describing the human and material costs of the current lead standard in drinking water is expected to be released next month. It was prepared to justify the imposition of stricter standards and was given to The Washington Post by a source seeking support for more stringent limits.

Lead contamination of drinking water varies widely from state to state, with Virginia and Maryland scoring well within the safety standard, the report said. No figures were provided for the District of Columbia, but District officials recently called the problem in one section, the Palisades, "urgent."

The primary source of lead in drinking water is the plumbing system of most American homes. Acidic, soft water disolves lead in the solder connecting copper water pipes, resulting in contamination of tap water. Although the EPA has regulated lead in drinking water since 1974, it rarely uncovered violations because officials monitor water at public places such as fire hydrants and treatment plants, rather than at homes with lead-soldered pipe connections.

After private firms testing for lead found much higher levels at home taps, the EPA last November proposed a significant tightening of its drinking water standard from 50 parts of lead per billion parts of water to 20 parts per billion. The proposal must overcome bureaucratic hurdles before it is adopted, and officials do not expect new lead regulations before 1990.

Reducing risks of lead contamination by bringing drinking water supplies into compliance with the proposed standard would cost as little as $ 3.80 per person annually, an EPA official said. It can be achieved by reducing the acidity and softness of drinking water, which contribute to lead pollution.

The report was based on more than 1,900 samples of drinking water in all 50 states, taken by government and private water testers over the past 17 years.

Average lead levels in the drinking water of seven states -- Arizona, Colorado, Florida, Illinois, Massachusetts, Michigan and New Hampshire -- exceeded the proposed standard of 20 parts per billion, according to the report. Illinois' average level was 87 parts per billion, the highest in the nation.

The average lead level in 18 samples in Maryland was seven parts per billion. In Virginia, the average level of 45 samples was six parts per billion.

The report, written by EPA economic analyst Ronnie Levin and updated by her in an interview yesterday, detailed the health consequences of lead levels at the current 50-parts-per-billion standard and concluded that 38.1 million of the 219 million Americans served by public water systems are exposed to greater health dangers because of the higher lead concentrations.

The report estimated that 8,100 children exposed to higher lead levels require medical treatment every year and 143,500 score from one to five points lower in IQ tests because of the neurological damage caused by lead consumption.

Lead contamination causes growth retardation in 36,400 children annually and blood ailments such as anemia in the same number, the report estimated. And it raises the risk of premature birth or low birth weights for 622,000 fetuses.

The same number of pregnant women between the ages of 15 and 44 face higher risk of such problems as placental membrane rupture. Another 34,000 women of the same age face a greater risk of reproductive problems.

Among white males aged 40 to 59, 370 die every year as a result of lead-induced health problems, according to the report.