WHEN HEW SECRETARY Joseph A. Califano Jr. unveiled the administration's drug-regulation bill the other day, he described it as "the most important piece of legislation in the health field to be sent up in many years." The usual hardsell, we note - but he could be right. The bill contains a complete overhaul of the law governing the ways in which drugs are tested and sold. If Congress passes it in anything like its present form, pharmaceutical companies will have fewer hurdles to surmount in putting new drugs on the market; the Food and Drug Administration will have more power to take dangerous drugs off the market, and consumers will have access to more information about the side effects of the drugs they take.

Given the fact that each of those aims is something the group benefitting from it has been seeking for years, you might think the bill would be regarded as a wondrous example of consensus legislation. And, HEW and FDA in fact tried hard to make it just that: The first draft, which grew out of a blue-ribbon commission study, was subjected to hearings, and efforts were made to reconcile objections to it. But the conflict between different parties in the drug field is so great that reconciliation was not possible. Thus, some drug companies and consumer groups have already denounced various aspects of the legislation and some legislators who will sponsor it on Capitol Hill intend to introduce major amendments.

Two basic facts account for the trouble. One is that no drug, not even aspirin, is absolutely, 100 percent safe; the other is that the development and testing of a new drug can be extremely expensive. Those who focus on safety want to make the pre-market testing of drugs as rigorous as possible; those who manufacture the drugs argue that if the testing procedure gets too rigorous, the rising cots will discourage the development of new drugs, and the protracted time involved will deny the benefits of new drugs to patients in need. Add to that the disclosures of the past decade concerning phony testing, weak law enforcement and deceptive advertising techniques, and the stage is set for a king-sized battle in Congress.

Our own impression of Mr. Califano's proposal is that it balances the competing interests quite carefully. The easier road to the market for the drug companies, for example, would be offset by the increased authority of the FDA to act if a drug's safety were to be called into question. Other aspects of the bill reflect other trade-offs. Some adjustments here and there may be necessary once all sides of the arguments have been fully presented. But it seems to us that the outline is there for a new law - an improve law that will keep the essential new drugs coming while giving the public the necessary reasonable assurance of safety.