Government regulators must issue by the end of September, a long-delayed set of standards restricting the amount of lead pollutants in the air, a federal judge in New York has ruled.

U.S. District Court Judge Charles E. Stewart Jr. on Monday ordered the Environmental Protection Agency to set nationwide standards for airborne lead in accordance with provisions of the 1970 Clean Air Act.

Although environmental groups and others have been pressing EPA for years to come up with such standards, a number of industries have bitterly fought proposals for tough airborne lead restrictions. A handful of states have laws covering airborne lead, with California the only one whose restrictions match the EPA proposal for a national limit of 1.5 micrograms of lead per cubic meter of air.

Lead in various forms has been labeled by federal researchers as the second most serious health hazard for children, after malnutrition.

In April the Carter for Disease Control in Atlanta reported that in areas with high levels of ingestible lead - such as inner-city "lead belts" of aging housing with lead-based paint - up to 20 percent of the children showed elevated lead levels in their blood.

CDC said largescale screening of children who did not exhibit lead-poisoning symptoms showed the number with high lead levels in their blood was greater than anticipated. The researchers said the effects of lead on children were "subtle" but could cause attention problems, learning disabilities or emotional disturbances.

EPA officials said yesterday they would comply with the federal court order to issue a lead standard by Sept. 30. But they said they did not know whether EPA Administrator Douglas Costle would approve a standard as strict as the one proposed by the regulatory agency in December.

Dr. Vernon Houk of the CDC yesterday said the federal order establishing a national ambient air standard for lead would be "a very major step" in cutting down the level of the metal that children would be exposed to in the future in lead-hazard areas.

EPA officials said that lead levels in the air around some heavy polluters such as lead smelters run several times above the proposed standard. The sharpest criticism of the EPA proposal has come from smelters, battery makers and the manufacturers of lead additives for gasoline.

Efforts to achieve a federal airborne lead standard date to 1973. In 1976 the U.S. Court of Appeals found then-EPA Administrator Russell Train in violation of the Clean Air Act for failing to initiate action on a national lead standard. Last December EPA issued its proposed lead standard, with a two-volume analysis of the problem.

A six-month delay allowed by federal law to issue a standard expired in June and the EPA was taken to court over the issue last month by the Natural Resources Defense Council, a New York-based environmental group.

The NRDC and the Environmental Defense Fund, another private environmental group, yesterday criticized the Carter administration's anti-inflation Regulatory Analysis Review Group for lobbying EPA officials after the close of the officials period for public comment and holding up a decision on the lead standard.

EPA officials said they had been approached by members of the review group about the potential cost of the standard to industry but they said the delay was caused by "machinations of the bureaucracy."