No public policy argument is so familiar and fatiguing, yet so central and urgent, as the decades-long battle over whether to focus more on the supply end of our illicit-drug problem or on the demand end.

I got into the issue 30 years ago partly in response to a call by now-Sen. Daniel Patrick Moynihan (D-N.Y.), then working for President Richard Nixon to stanch the flow of illegal drugs at the "source." The State Department's traditional indifference to engagement in gritty law enforcement seemed to Moynihan, and in turn to me, as outdated and dangerous. He had a role in the Nixon administration's experiment with supply interdiction: It produced what he now acknowledges to be "at most a brief success" in closing down the "French Connection," while "opium and heroin production merely moved elsewhere."

This is pretty much the story of supply interdiction since then. Prodigies of law enforcement are overwhelmed by the ease with which traffickers can meet a seemingly insatiable American demand. Moynihan confronted the political reality behind policy as a U.S. senator in 1988 while working to focus new drug legislation on users. Some 60 percent of the money was to be earmarked for demand reduction, 40 for supply reduction.

But, Moynihan now relates, "as the bill made its way through House and Senate deliberations and quasi-conference committee negotiations, its emphasis shifted incrementally from demand reduction to supply reduction and, especially, to law enforcement. I suppose this was inevitable. Fear of crime far outstripped concern for addicts. And just a few weeks away from the 1988 elections. . . . The deal was a 60-40 ratio in favor of demand reduction; in the end it was the other way around. Now the ratio is about two-to-one the other way."

This episode and much else shaped the conclusions he presented at a Yale conference on the century of American experience with heroin. "While the science of drug abuse and addiction holds great therapeutic promise," he said, "the politics are self-defeating, punitive and vainglorious."

What? The science of drug abuse and addiction holds great therapeutic promise? An emphasis on cutting down the demand for illegal drugs, on focusing on users rather than producers and traffickers, appeals to many of us who are frustrated by the shortfalls of law enforcement and troubled by the foreign-policy complications of a supply-oriented strategy. Up to now, however, there don't appear to have been the research breakthroughs that would make a treatment-oriented policy a medically, economically and politically feasible alternative to sending in the cops.

I am not a student of the science, but let me cite Moynihan and one of his gurus:

Moynihan: "Ours surely is the great age of discovery in the field of neuroscience. We are exploring the brain, not least with respect to the effect of drugs. . . . I think it safe to assume that we may never win a `war' against drugs. Perhaps the closest we can come, through scientific research, will be to identify `pre-exposure' vulnerability in the population and develop some sort of active or passive immunization. We're making progress. . . . Supply interdiction doesn't work, although absent it things could be even worse. We spend twice as much on it as we do on biomedical research. But the latter moves."

Alan Leshner, director, National Institute on Drug Abuse: "If we know that criminals are drug addicted, it is no longer reasonable to simply incarcerate them. If they have a brain disease, imprisoning them without treatment is futile. If they are left untreated, their recidivism rates to both crime and drug use are frighteningly high; however, if addicted criminals are treated while in prison, both types of recidivism can be reduced dramatically. . . .

"Understanding addiction as a brain disease explains in part why historic policy strategies focusing solely on the social or criminal justice aspects of drug use and addiction have been unsuccessful. They are missing at least half of the issue. If the brain is the core of the problem, attending to the brain needs to be a core part of the solution."

Moynihan: "The outcome of narcotics prohibition over the past century has been to concentrate drug abuse and addiction principally among an urban underclass most don't know and for whom there is currently little public understanding or sympathy. So Congress and the public continue to fixate on supply interdiction and harsher sentences (without treatment) as the `solution' to our drug problems, and adamantly refuse to acknowledge what Dr. Leshner and others now know and are telling us."