''Every time a dairy farm dies, an angel gets his wings.'' No, that's not right, is it? ''Every time a dairy farm dies, consumers and taxpayers save $61,885.'' True, but that can't be what they intended to say. Ah, yes: ''Every time a dairy farm dies, part of Canada dies, too.''

The hysterical reaction from the dairy industry, as in the above slogan, to a proposal to limit imports to 5% of the market instead of 2.5%, does much to explain why the current round of world trade talks are heading for collapse. So does the government's too-clever-by-half attempt to have other countries slash farm subsidies, while our own supply management systems in dairy and poultry products remain, import quotas and all. Enough has been written about the absurd costs of the agricultural war - $300 billion in subsidies and other payments annually worldwide, $8.8 billion in Canada alone. By now, most informed readers are probably aware that Canada spends more propping up agriculture than all other industries combined, that it costs us $100,000 for each farm job ''saved,'' and so forth.

Yet despite the almost universal agreement that this is madness, the likelihood is that when trade ministers from the 99 members of the General Agreement on Tariffs & Trade meet in Brussels in December, after four years of negotiations, they will have failed to reach any substantial agreement to dismantle their protectionist arsenals.

One hesitates to make such predictions - brinkmanship dictates that concessions be kept in hand until the last possible moment - but no one's bluffing on this point: if there's no deal on agriculture, there's no deal on the rest of the GATT's agenda. Given the inability of members of the European Community to agree among themselves even to a 30% cut in subsidies - and that from record 1986 levels - the brinksmen may find their momentum carries them over.

If so, then Canada is going to face hard questions. The sole defence for shoveling billions of borrowed dollars into a small, declining industry was that it would force the Europeans to come to their senses - or at least tide our farmers over until the Americans did the job for us. But now that it's clear the EC, at last revealed as the Franco-German farmers' collective it always was, will not ever come to its senses, what argument remains?

Likewise, the justification for negotiating with other countries to reduce our own subsidies and other trade barriers, though they impose costs on Canadians far in excess of any damage they do our trade partners, was that it would create an external constraint with which the government could ward off the protection lobby at home. Clearly, it has not: rather than binding itself with treaties, the government has wriggled out of such commitments as it had made, whether to the Cairns Group of agricultural exporters or the GATT itself. It is as much a prisoner of the farmers as before.

We see before us the collapse not only of the GATT, but of the whole negotiated approach to trade liberalization. The insistence on reciprocity has always been a puzzle to economists, for whom the benefits of free trade in one country have never depended on like action by its partners, though they would be magnified in such event. Cheap imports, from whatever source, are a boon: The subsidy war pits the nations of the world only in a furious competition to see who can send the most foreign aid to each other's consumers.

But reciprocity is not only an intellectual curiosity: it is inimical to free trade. This has most usually been evident on the home front. The insistence on trading off concessions that aren't really concessions instills in the public mind the notion that something good is being given up. The constituency for protection is created by the very process designed to reduce it. So why talk about it? Trade liberalization, after all, isn't like nuclear disarmament.

Maybe it should be. The lesson of recent times is that reciprocity isn't even a very good strategy for lowering other countries' trade barriers. For 40 years, similarly, U.S. and Soviet negotiators sought to rein in the arms race with arms- control agreements, with little success. The breakthrough came with Mikhail Gorbachev's bold unilateral reductions: the ''peace offensive.'' Not only were they brilliant public relations - increasingly important, in a populist age - but they left the Soviets free to reverse them at any time. Western hawks groused that this made them worthless. In fact, it made them permanent.

Sooner or later some smart cookie in International Trade will see the advantages of unilateralism, not only as a last resort, but as a first strike.