THE PROPOSAL for a government-held reserve of wheat to be kept for overseas famine emergencies is an idea whose time may finally have come -- after 25 long years. Throughout that period the United States has distributed a good bit of food aid but always by waiting for the crisis and then buying the food in the market. Farmers, suspicious lest the government buy food ostensibly for a famine reserve and then release it when domestic prices are high, have prevented the government from accumulating a stock to have ready when an emergency strikes.

This year, however, there was a quirk in the pattern. To prevent farmers from getting stuck when he embargoed certain grain exports to the Soviet Union in the Afghan crisis -- exports that, regrettably, many in the Congress now wish to resume -- President Carter had the government buy up four million metric tons of wheat. Unless something is done with it, that wheat will eventually be released back into the market. To forestall that, farmers suspended their opposition, at least this time around, to a government-held reserve. Budget watchers were reassured by knowing that the money to buy the wheat had already been spent. The anti-hunger lobby naturally was pleased. The House and the Senate both agreed.

But of course there's a hitch. The reserve is part of a child nutrition bill that is hung up in conference for unrelated reasons. A strategy has been devised under which the reserve would be unhitched from this bill and attached to a measure on grain inspection. The House is willing to make the switch. The Senate is about to decide.

Let there be no surge of self-congratulation over the prospect of the United States' finally doing the sensible and responsible thing in putting itself in a position to allot food promptly to people facing starvation. Four million tons, the size of the reserve now proposed, is no grand amount. It would provide no more than a mean subsistence diet for a year for, say, 15 million people. One bad crop failure in a bigger country, two or three failures in smaller countries, could wipe out the reserve. The food is something, however, and the precedent of government readiness is valuable.

There is a broad discussion going on in world agricultural circles these days about the urgency of food self-sufficiency. It is widely accepted that at some times and places food aid, even when it has not been used as a kind of political slush fund, has sapped local efforts to grow more food. But it is not possible to foresee a world in which genuine food emergencies will not recur, and the United States is right to be moving toward an official reserve to help out.