Because chemical weapons kill so indiscriminately and massively, their use has been outlawed since 1925 under international agreement. Though Iraq signed the agreement, that hasn't kept Baghdad from violating it at least four times since 1984. Now it has committed another grisly violation.

Two weeks ago, Iraq wiped out 5,000 people many of them women, children, and old men and injured 5,000 others when a single warplane dropped a mixture of mustard and cyanide gases on a renegade Kurdish province of Iraq that has welcomed its capture by Iran.Though the need to deter wartime collaboration is understandable, it does not excuse the barbarism of this particular episode nor Iraq's repeated treaty-breaking.

What has the rest of the world done about this latest outrage? Nothing unless you count a little impotent tongue-clacking in a few big power capitals and at the United Nations.

That won't do at all. Neither will current U.S.-Soviet negotiations at Geneva on a new agreement to reaffirm the ban on the use of chemical weapons, outlaw their production, and call for the destruction of existing stockpiles.

If Iraq is allowed to get away with mass murder, other nations must assume that their enemies might be tempted to use chemical weapons. How much trust, then, can the world place in international agreements, old or new?

Iraq is said to have the largest stockpile of chemical weapons in its part of the world. Among them are poison and nerve gases that Iraq produces itself. For its part, Iran also is believed to have its own less sophisticated chemical weapons mainly phosgene and mustard gases easily made from readily available industrial components. In addition, Iran may be getting chemical weapons from Syria. The U.S. State Department thinks Iran may already have used its chemical weapons against Iraq.

If the United Nations won't do more than just admonish Iraq with another warning like the four that Iraq has ignored since 1984, the super-powers should take matters into their own hands. Washington and Moscow should tell Baghdad to stop using chemical weapons or forfeit all U.S. and Soviet support.