WHEN CONGRESS tried to write a new federal pesticide law in 1982, one issue over which it stumbled was states' rights -- whether anxious states should be able to exceed federal regulations with stiffer laws of their own. Now, in somewhat different form, the issue has arisen again.

A major problem in pesticide regulation is that many chemicals now in use were approved years ago on the basis of suspect standards that no longer pass muster. The Environmental Protection Agency was told in 1972 to review these old approvals. In the 14 years it has had the job, it has made its way through only about 40 of the 600 active ingredients involved.

This year the country's major chemical companies and environmental groups reached a remarkable accord on procedures to speed up this review. A new pesticide law seemed possible. The House Agriculture Committee reported out a version last month, 42 to 1. The Senate committee is supposed to mark up another this week. But time is short before adjournment, and the nation's grocery manufacturers have raised the state "preemption" issue.

On two recent occasions, involving first the fumigant EDB, used heavily on grain, and now the growth regulator daminozide, used particularly on apples, state regulators have moved ahead of EPA to ban or limit use. The grocery manufacturers see the possibility of more such free-lancing in any serious review of the nation's pesticides, as contemplated in the current bills. A crazy quilt of state regulations as to permissible pesticide residues on food would make it enormously difficult for national food companies to do business. The grocery companies would basically limit the right of states to regulate to emergencies only. The House committee actually agreed to such an amendment, then dropped it for fear of complications before the bill reaches the floor.

Those resisting the amendment note that states have preemptive rights under other major environmental statutes which they have not abused; that competition can only be good for a federal agency with a record so sluggish as EPA's on pesticides; that EDB and daminozide are the only examples the grocery manufacturers can point to, and that the time to solve the crazy-quilt problem is when it occurs. Right now, this argument goes, the greater risks are on the other side. That seems right to us.