On numerous occasions last year the amount of lead in the air in the District of Columbia exceeded federal clean air standards, according to a report by the city's Department of Environmental Services.

During the first three months of the year the average amount of lead in the air sampled at all nine city air quality monitoring stations exceeded the federal limit. During the third quarter, the limit was exceeded at three of eight operating stations.

District environmental health director Bailus Walker said he doesn't know what the health effect of this is, other than the fact that the federal standard of 1.5 micrograms of lead per cubic meter of air was based on the belief that higher levels of lead are unhealthy.

Elevated levels of lead in the blood -- particularly in children -- are believed by some researchers to cause neurological problems ranging from minor learning disabilities to a lowering of the IQ or even to coma and death.

Blood lead levels in children are generally highest in the summer when they are outside playing and have more contact with dust and dirt, which may contain airborn lead. Althought most childhood lead poisoning was thought to be a problem of the inner city, primarily caused by eating lead paint chips, recent conflicting studies in Washington have found that between 3 and 40 percent of the children surveyed in affluent upper Northwest Washington have slightly elevated blood lead levels.

In the first three months of last year the lead levels at the nine stations ranged from 1.90 micrograms to 3.83. All but one of the stations averaged more than 2 micrograms per cubic meter of air.

According to Walker, most of the District's airborne lead is generated by automobiles using leaded gasoline, which account for an estimated 50 percent of the automobiles on District streets.

Virtually all autos manufactured in 1975 or later require unleaded gasoline. But Walker said his department estimates that 10 to 15 percent of the 1973 to 1978 cars "have been tampered with or altered in some way" to allow them to use leaded gasoline, which is generally a few cents cheaper per gallon than non-leaded fuel.

"We feel it is important for District motorists to know about the damage they are doing to the environment as well as the potential cost of automobile repairs," said DES director Herbert L. Tucker.

By January 1982, the District, Virginia and Maryland are all expected to begin inspecting automobile polution control systems as part of their inspection programs. Such inspections would detect any tampering with the system, officials say, and correcting the alterations could cost the motorist $150 or more.

Under the terms of the federal Clean Air Act, any mechanic who knowingly alters a car's polution control system, such as removing the catalytic converter, can be fined $2,500.

According to Walker, when DES inspectors were in District gas stations recently checking on the operation of the pumps, they saw "any number of cars using leaded gas when the cars weren't designed to use it."

Walker said he does not know why there is so much variation in the quarter-to-quarter air-lead figures. "There are just too many variables," he said.