A year has passed since President Reagan first called for the world-wide elimination of all farm subsidies and trade barriers.

Since then, the response to this ambitious proposal has ranged from lukewarm at best to outright hostility.Even so, Mr. Reagan ought to keep pushing the plan in the next few days when the world's industrialized nations hold their annual economic summit conference in Toronto.

Why keep beating a dead horse? Because this particular steed is starting to show new signs of life.

Just how much life is indicated by The Los Angeles Times, which recently reported growing sympathy for a global end to farm subsidies in Western Europe, where "the almost intolerable burden of the subsidy programs is finally forcing government leaders to pay attention."

In the European Economic Community, about $28 billion a year is spent on subsidy programs serving 12 million farmers. By contrast, the United States is spending nearly $18 billion this year on 2.3 million farmers.

But those figures don't give the entire picture.

A big part of the picture consists of the fact that the biggest subsidies, in Europe as well as in the U.S., go to the richest farmers who need such help the least.

Another part of it consists of the fact that some of the subsidies underwrite farm exports that allow sales at prices as much as 30 percent below the actual cost of production. While this helps reduce big and costly crop surpluses, the practice also distorts the world market and hurts other exporting nations with little or no farm subsidies.

Still another part of the picture consists of the trade barriers that force consumers to pay artificially inflated prices. In the case of Japan, for example, consumers there pay as much as 10 times the world price for rice to protect Japanese growers from international competition.

What harmful folly!

If agriculture were free of subsidies and trade barriers, American farmers likely could regain some of the world markets they have lost in recent years. Because of their high degree of efficiency and productivity, American farmers can compete well - as long as the playing field is level and they don't have to struggle uphill against artificial impediments.

The U.S., of course, can't afford to abandon all farm supports unilaterally. It would be too harmful to American farmers unless other major agricultural nations drop subsidies, too.

Meanwhile, if other nations object to the Reagan version of the proposal or can't meet the turn-of-the-century deadline, let them offer their own plans for phasing out farm subsidies. A good place to do so would be during the coming economic summit in Toronto.