Existing evidence on the toxicity of airborne lead would justify a complete ban on leaded gasoline, a three-judge panel of the United States Court of Appeals for the District of Columbia said yesterday.

In language that some attorneys interpreted as inviting the Environmental Protection Agency to institute such a ban, Judge Patricia M. Wald wrote, "the demonstrated connection between gasoline lead and blood lead and the demonstrated health effects of blood lead . . . would justify EPA in banning lead from gasoline entirely."

The unusual statement came in a unanimous opinion upholding the agency's ceiling on permissible lead levels in leaded gasoline. Small refiners had challenged the agency's requirement that they meet an interim ceiling on the lead content of their leaded gasoline; the court accepted this argument of the small refiners.

More than half the gasoline produced in the United States is unleaded, largely because lead ruins the catalytic converters mandated by EPA in later-model cars. Catalytic converters are designed to control emissions of other pollutants.

The ruling comes as the EPA is laying the groundwork for new rules limiting the concentration of airborne lead. The existing rules on concentrations of six separate air pollutants are reviewed every five years.

In addition to the statement encouraging a ban on leaded gasoline, the opinion said that a review of scientific evidence indicates that it may take less lead than previously thought to present a "significant risk of adverse health effects" in children.

Noting that the current "recognizable danger point" of blood lead levels is 300 micrograms per liter of blood, the opinion said "recent studies suggest that the recognized danger point . . . is too high and that lead reduces intelligence at blood lead levels as low as" 100 to 150 micrograms per liter of blood.

It added that, if the danger point really is as low as 100 micrograms of lead per liter of blood, half the children in the United States would face the risk of lead poisoning.

While upholding EPA's ceiling levels for lead in gasoline, the court said the agency offered little justification for the standard.