Jimmy Carter won't have too trouble countering many of the complaints against his administration in the new Republican platform, but it's not going to be easy to make the GOP nominee eat his indictment of the president's grain embargo against Russia.

In calling for an end to that policy, Ronald Reagan said, "For months now, America's farmers -- singled out from the beginning by the Carter administration to bear the major brunt of the embargo -- have suffered alone and paid a terrible price." The record, he says, is clear: "The embargo has had virtually no impact on the Soviet Union."

Reagan was not exaggerating. The president's own Department of Agriculture concedes that the Russians have had no difficulty filling their grain needs by buying it elsewhere. Even U.S. allies, like Canada and Australia, have not hesitated to sell the Soviets millions of tons of grain. So Carter's show of "punishing" Russia for its Afghan aggression has ended up with America's farmers and taxpayers being the real victims.

The Farm Bureau Federation, which, in a burst of patriotism, originally supported the embargo, now charges that the president has not made good on his promise to prevent financial losses to the farm community. The situation is aggravated by the recession. This year, it is estimated, net income of U.S. farms will probably fall by one-third, to around $22 billion -- the sharpest one-year drop in over 50 years.

The president keeps saying that "everything we have done against the Soviets is effective," but Business Week reports that he is "groping for a face-saving way out" of the embargo. The administration recently gave U.S. grain traders a green light to use foreign subsidiaries to ship non-American grain to the Soviets and officials are now dropping hints of a further relaxation of the embargo late this summer.

There is little doubt that political pressure for a change of policy will increase, but up to now Carter's public response to Reagan has been to say, "I think we ought to punish the Soviet Union for their [Afghan] invasion and convince them that aggression in this world does not pay."

In the view of most of our allies, however, there is little to be gained by ineffective reprisals such as the grain embargo and the porous ban on the sale of technological equipment to Russia. The Olympic boycott inspired by the United States may be an embarrassment to Moscow, but it has also generated an embarrassing schism in the Atlantic alliance.

While our staunchest European ally, West Germany, finally and grudgingly supported the boycott, Chancellor Helmut Schmidt openly questions the practicality of "punishing" the Soviet Union for its actions in Afghanistan. pHe feels such a policy is unproductive, if not counterproducutive, and could be dangerous as well.

Rep. John Anderson, after a tour of Europe, said he found a concensus among the leaders he met that the "door must be left open to resume diplomatic discussions" with Moscow. The independent presidential candidate believes nuclear weapons are so great a threat to civilization that the United States should resume disarmament negotiations after the Nov. 4 election even if Russian troops are still in Afghanistan.

Few seem to remember, but that is the policy the American government followed after Soviet troops quelled the Czechoslovakian revolt in August 1968, which also was a presidential election, both the outgoing president (Lyndon Johnson) and the incoming chief executive (Richard Nixon) moved to activate arms limitations negotiations (SALT I), although Soviet troops were still in Czechoslovakia, as indeed they still are today.

Giovanni Agnelli, the head of FIAT and former chairman of the Italian Federation of Industry, warns that the United States and the West are facing hard times. "Detente between the superpowers has come to a standstill," he says. "World peace is in jeopardy and the stakes now can be more hazardous than ever before." He does not single out Carter for all the blame. He thinks the worst mistake was the failure of the United States and Japan to cooperate with the Soviet Union on the development of the oil and gas fields of eastern Siberia. That deal was allowed to lapse through several U.S. administrations.

In a knowledgeable new book ("Of Blood and Hope"), Samuel Pisar, a former U.S. economic adviser, strongly supports Agnelli's view that the failure of the Siberian deal was a bad day for world peace. "Any policy that seeks to reduce the Soviet Union's access to energy at home," Pisar says, practically invites the Red Army to the Persion Gulf and constitutes an added danger to our security and welfare."