In the face of intense protests, the Environmental Protection Agency apparently has done an about-face on the issue of lead standards for gasoline and is preparing to toughen, rather than relax, the restrictions on leaded gas.

EPA sources predict that the new proposal will reduce the amount of lead in the air by 31 percent more than the current standards would over the next eight years.

"EPA has determined that rescinding or relaxing the present lead standard would result in an increase in lead emissions to the atmosphere" and that "environmental lead exposure continues to be a national health concern," EPA explained in a notice scheduled to be printed in the Federal Register in the next several days.

An earlier agency proposal to relax the standards, made public in February, brought a storm of denunciations from health-interest groups and environmentalists.

Ellen Silbergeld, a toxicologist with the Environmental Defense Fund and an outspoken critic of EPA's original attempt to relax the standard, said, "We're very pleased that they withdrew the February proposal."

However, Silbergeld said she had "certain problems" with the new plan and that some revisions will be needed to ensure that the new plan will result in the drastic cut in airborne lead claimed by the agency.

Lead, long known to have adverse health effects, particularly on children, is added to gasoline to raise the octane level.

Under the current system, the average amount of lead added to gasoline by large refiners must not be more than 0.5 gram per gallon (gpg) of all gasoline (leaded and unleaded) they produce. For small refiners the limit ranges from 0.8 to 2.65 gpg, depending on the size of the operation.

This system allows a refiner to increase the amount of lead it adds to its leaded gasoline each time it increases its volume of unleaded gasoline. Recent studies indicate that the overall amount of lead in gasoline has been rising, due in part to this system.

EPA's new proposal would regulate the lead in leaded gasoline only. Large refineries would be permitted to add 1.10 gpg, and small refineries would be allowed to add 2.50 gpg.

This would force most large companies to cut back on lead usage, but EPA noted that it might allow some companies that have never produced much unleaded gasoline to increase the amount of lead they use. The agency does not view this as a problem, but Silbergeld does not believe any increase should be allowed.

Small refiners have enjoyed a special status under the old regulations, but that status is scheduled to expire Oct. 1. EPA has proposed keeping a special category, but significantly tightening its definition of small refineries. The change would reduce the number of firms eligible for the special status from about 159 to 74, according to EPA officials. They expect the change to cut off a majority of the so-called blenders, who add large quantities of lead to inexpensive gasoline components. The blended gasolines are considered a major source of new airborne lead.

One EPA proposal that Silbergeld sharply criticized is the agency's plan to let all refineries average their lead usage. Referring to it as a sort of "bubble plan" for lead, EPA wants to allow one refinery to increase the amount of lead it uses, if another refinery will decrease its lead use by the same amount. The refineries can be owned by the same or different companies and can be in different parts of the country.

The agency has also proposed placing imported gasoline under the same lead standards as domestically produced gasoline. Currently, gasoline produced abroad escapes lead regulations. The agency also moved to resolve a minor controversy over the way it calculates lead content. It used to permit refiners to round the 0.5 gpg standard to 0.549. EPA plans to set the level at 0.50 gpg.