The Environmental Protection Agency yesterday proposed modifying the rules for reduction of lead content in gasoline to allow refiners to leave more lead in than new limits allow if they begin removing it from their gasoline ahead of schedule.

Under the proposal, which is subject to public hearings and formal approval, refiners could make gasoline with less lead than federal limits now allow and "bank" the difference, using the credits in 1986 and 1987 when lead standards become more stringent. The banked credits also could be bought and sold between refiners.

EPA officials said the net effect of the plan would be to reduce led content in gasoline, while giving refiners flexibility in modifying refineries to handle the new requirements.

"The reduction of lead in gasoline is critical to the protection of public health," said EPA Administrator William D. Ruckelshaus. "It is important, therefore, that practical measures be taken to assure that the refining industry can realistically achieve the standards which the agency has proposed."

Last summer, the EPA announced plans to phase down the lead content in leaded gasoline over the next three years from the current allowable 1.1 gram of lead per gallon to 0.1 of a gram per gallon. The agency says a more comprehensive package of lead phasedown rules will be released within the next few weeks.