LEAD IS ONE of the most potent poisons in the human environment. Experts believe that there may be no safe level of lead in the body and that levels found in cities may permanently impair children's mental development. Ninety percent of airborne lead, however, comes from automobile emissions and can be controlled by lowering the amount of lead in gasoline, for a fraction of a cent per gallon. Such a program has been long under way and was to have reached its final stage next October.

But last year the petroleum and refining industries, which had resisted this program through three administrations, found a receptive ear. The White House Task Force on Regulatory Relief directed the Environmental Protection Agency to review the program. EPA responded with a formal proposal to relax or rescind the lead standard.

That was bad enough. There are few federal regulations for which the scientifically established need is clearer, the advance warning given to industry longer (nine years) or the cost more reasonable in relation to the benefits. An open-minded review at EPA would have established these facts and revealed also that changing the standard at the last minute would punish the great majority of refiners that had complied with the law.

But it seems that before EPA had heard a single witness, Administrator Anne Gorsuch had already addressed the question. Last December, she met privately with representatives of Thriftway, a small refinery that wanted a waiver from the upcoming standard. Witnesses have confirmed in sworn testimony to EPA's inspector general that Mrs. Gorsuch rejected the waiver request because it would invite a flood of other such requests. But she promised that Thriftway would not be prosecuted for violating the standard because the agency intended to abolish the regulation in 1982. According to a Thriftway lawyer, Mrs. Gorsuch spoke privately to a Senate aide who was present and "explained to him that she couldn't actually tell us to go out and break the law but she hoped that we had gotten the message."

Rep. Toby Moffett, who prompted the inspector general's investigation, later wrote the president requesting disciplinary action against Mrs. Gorsuch for granting preferential treatment to a single company and for corrupting the rules that an agency is supposed to follow in reaching a decision based on the evidence. Mr. Moffett had discovered that, before announcing its proposal, EPA had held 32 meetings with representatives of the petroleum industry and no comparable meetings with health experts.After six weeks, the White House has not responded.

There is more. Prompted by a rise in the amount of lead in refined gasoline beginning in the third quarter of 1981, the Center for Auto Safety investigated. It revealed this week that in 1981 EPA began informing refiners that it would allow them to exceed the lead standard by almost 10 percent. EPA says that it is merely a matter of "rounding off" a number and that this was not a new policy.

There has been so much opposition to relaxing the lead standard that EPA may be forced to drop its plan. But the matter cannot end there. Mrs. Gorsuch should accept the necessity of recusing herself from the lead proceeding because of the Thriftway incident, and of enforcing existing regulations. The president should see to it.