AMONG THE many bills dropped into the hopper on the Senate's first day in session was a measure sponsored by Sen. Daniel Inouye that would allow heroin to be used to relieve the pain of dying cancer patients. A similar bill had been expected to clear Congress last year. But the House defeated it in an attack of pre-election cowardice brought on by opponents' baseless charges that the measure would contribute to illegal drug abuse.

The bill's cosponsors already include Dennis DeConcini, Ernest Hollings, Steven Symms, John Warner and Don Riegle. Their views do not normally coincide, but they share a compassion for the thousands of dying people whose severe pain could be alleviated by controlled injections of heroin. None of these senators -- or the large bipartisan group of House members who cosponsored a similar measure last year -- could possibly be accused of being soft on drug abuse. Having studied the measure's safeguards, they simply recognize that the very small amount of heroin needed by hospitals and hospices could not, even under the most dire and improbable scenarios, add in measurable degree to the vast street trade in illegal heroin.

These congressmen have also considered the proven, unique effectiveness of heroin in treating certain patients. The many physicians in Great Britain who now prescribe heroin, preferring it to other painkillers, have sworn to its good results, and so have experts on pain therapy in this country. They are also aware that there is no evidence that Dilaudid-HP -- also an addictive opiate but one preferred by the Reagan administration apparently because its name is not commonly associated with illegal drug use -- is as effective as heroin or has as few side effects.

Despite the billions spent on novel therapies and other medical research, remarkably little is known about the treatment of pain. And yet most people would put pain relief at the top of their priorities for the treatment of themselves and their families. But it is known that different people respond differently to painkillers, so the wise physician will want to have as many options available as possible. If, after the experimental period set by the bill, heroin were not found more useful than other known or newly developed drug, authority to use it would expire automatically.

Under pressure from physicians, the Canadian government recently decided to legalize use of heroin to treat pain, and a similar move is under way in Australia. It would be a shame if Congress failed to act promptly to provide similar relief in this country.