IN WILLIAM D. Ruckelshaus, the White House has found a strong and experienced administrator to take over the Environmental Protection Agency. Once again, President Reagan's second choice turns out to be decidedly better than his first. Mr. Ruckelshaus is a political conservative whose recent career in the lumber industry will doubtless have given him some sympathy for a businessman's side of environmental issues. But he is a man with a firm sense of the laws' integrity, and he is not likely to try to subvert them by simply refusing to carry out their requirements. That will be an improvement over the EPA's recent style.

Having been at the EPA when several of the most important of those laws were enacted, he knows that there are good reasons for them. He is not likely to confuse the realities of the subject with the rhetoric of the 1980 presidential campaign. And he has still another advantage over his unfortunate predecessor. He will be working for a White House that has learned, at rather high cost, that the support for the principle of those laws is much stronger in Congress and around the country than it had thought.

As Mr. Ruckelshaus takes up this arduous job, he will be in a position to ask for support from Congress--including all those subcommittees now jostling each other to get in front of the television cameras. Much of the basic environmental legislation is in great need of revision. Restrictions on some pollutants--automobile exhaust, for one--have turned out to be tighter than any health hazard would justify. Other and more dangerous kinds of pollution are controlled badly or not at all. Ambiguities have appeared. The Clean Water Act declared 13 years ago that the discharge of toxic pollutants was to be flatly prohibited. It seemed sensible at the time, but the chemists have now found that some toxic contaminants are created by the water purification process. And what, exactly, is a toxic pollutant? As the Conservation Foundation recently observed, "Many substances may be toxic at high concentrations but relatively innocuous, or even necessary to the maintenance of good health, at low concentrations."

One compelling reason for ending the warfare over the EPA is to create an atmosphere in which Congress can review the enormous body of legislation that it has created, and revise it in the light of current knowledge. That can happen only under a strong administrator who is capable of persuading the congressional committees that he is dealing with them in good faith. Mr. Ruckelshaus' job really comes down to that--rebuilding a presumption, not only in Congress, that the EPA is dealing in good faith.