THE NATION'S most serious environmental problem may be the one the government is doing least about. That is the dousing of the land and food supply with pesticides. The trend of neglect seems likely to continue this year. Legislation to give some life to the near-dead regulatory process appears to be slipping. The more immediate problems of the budget and farm credit system have taken precedence in the agriculture committees.

The shaky truce between the chemical companies and environmental groups that almost ended in compromise in the last Congress has reverted to the adversarial relationship that produced the stalemates of the past. The Senate Agriculture Committee may yet report a bill this year. But further action in the Senate and House will apparently have to occur amid the distractions and crowded calendar of an election year. It is not a happy prospect.

The present system of regulating pesticides was set up in 1972. The brand-new Environmental Protection Agency was to have the jobs both of regulating new pesticides and reevaluating by modern standards the old ones already on the market. The old ones -- there are about 600 active ingredients -- still constitute the bulk of pesticides in use. But the agency has worked its way through only a handful. It is almost as if the 1972 law had never been passed.

Last year's compromise and this year's tentative Senate bill would shorten the reapproval process and set deadlines. All the old chemicals would have to be reevaluated within nine years. That would be by 1997, 25 years after passage of the initial act, a period during which pesticide use and exposure will have steadily increased. That hardly seems too much to ask.

Because cost has been made an issue, the bill would impose fees on the chemical companies to help finance the program, and would reduce the large indemnities to which the law now entitles them if their products are banned. But the companies would be given some patent concessions in return. The legislation would also require the states to take steps against the leaching of pesticides into groundwater, an increasingly serious problem. And foreign buyers of U.S. pesticides would have to be made aware of limitations on their application here.

It is hard to imagine legislation much tamer or more necessary than this. Even so it has met resistance. Opponents are even seeking to use it in some respects to weaken existing law. They would reduce the right of states to set higher-than-federal regulatory standards of their own. That would be wrong. The states have been the major source of regulatory energy in recent years. Instead of turning the state motors off, Congress should turn the federal motor on. It is mindless to keep using these potent chemicals without a closer look at their effect