We are writing in reply to a June 22 Rowland Evans and Robert Novak column {"The War in the Andes"} purporting to comment on a report prepared by the National Defense Council Foundation.

We wish to make the following points: Our two governments are working closely with the government of the United States in the anti-coca effort, but all decisions as to how this effort will be conducted inside our respective countries are the exclusive province of our governments and will be made by our leaders. By signing up for the war on drugs, we do not -- and have not -- waived our sovereignty. Respect for that sovereignty is fundamental to the success of our common effort. The use of herbicides to destroy coca plantations is only a U.S. option. That strategy does not take into account the human, economic and environmental costs of such a pervasive use of deadly poisons. There are other, better ways to deal with this problem. For the United States to develop a "contingency plan" that contemplates "unilateral" action would be an outrageous intrusion on the sovereignty of our two nations and would destroy the working partnership that now exists. We are confident that the government of the United States would never entertain such a course of action.

Messrs. Evans and Novak are clearly in need of a full and accurate report about the progress that has been made in our common work to rid this hemisphere of the scourge of narcotics trafficking. We would of course be happy to provide them with such a report. Without an understanding of what has been tried already, what has in fact been accomplished and what is being done today, it is irresponsible to recommend drastic measures that can only do damage to the historic partnership that now exists between the governments of the Andean nations and the government of the United States. CESAR G. ATALA Ambassador of Peru JORGE CRESPO-VELASCO Ambassador of Bolivia Washington

I have worked in agricultural development in the Huallaga Valley of Peru for the past 20 years, most recently for the Agricultural Commission of the Peruvian Senate. I must express my amazement at the superficiality and insensitivity of the June 22 Rowland Evans and Robert Novak column on supporting aerial spraying of the new herbicide Spike to eradicate coca fields in the Upper Huallaga Valley.

I will avoid in this brief comment raising questions of ethics or human rights and limit myself strictly to the practical and economic aspects of the proposal for forced eradication of coca fields though chemical herbicides. To eradicate through aerial spraying the 200,000 hectares {772 square miles} now devoted to coca production in the Upper and Middle Huallaga Valleys would require spraying a total of 3,000,000 hectares {11,583 square miles, which is approximately the size of Maryland and Delaware combined}, an area 15 times that targeted. This is due to the dispersion of the fields throughout an immense mountainous territory covered with forest, which is totally cloud-covered 80 percent of the year.

An operation of this size would require an enormous fleet of airplanes and hundreds of thousands of gallons of herbicide, would cost many human lives and would take many months of work finally to achieve the defoliation of a vast land area in which a 130 inch per year rainfall would produce total destruction through erosion and flooding with an impact extending to Brazil.

Moreover, nothing would prevent the present cultivators from moving to other part of the Peruvian jungle (the Upper Huallaga makes up only 5 percent of its extent) and rapidly reestablishing their operations. This would lead in turn, if this policy is to be effective, to successive new plans for aerial spraying, until the entire Amazon basin is destroyed.

The report, in addition, grossly misunderstands Peruvian reality when it implies that the country's economy is dependent on coca, thus supposing that the flow of illegal foreign exchange into Peru is beneficial. Quite to the contrary, no country would benefit more than Peru from the disappearance of the drug trade, but this is no reason to undertake a violent and irrational experiment like the use of Spike.

The Huallaga Valley is Peru's principal producer of corn and its second producer of rice for internal consumption, but its conventional agriculture has been brought to a standstill through a combination of competition from coca, terrorist destruction of roads, collapse of the local government and financial system and impractical government economic and pricing policies. Peru now imports corn and rice from abroad.

A great opportunity exists at this moment to reactivate non-coca agriculture in the valley through a combination of sound assistance aimed at the key bottlenecks: lack of farming equipment, seeds, pesticides, fertilizer and transportation. The disruption of the drug trade in Colombia has caused coca prices paid to producers in the Upper Huallaga to drop to half of previous levels, providing a real window of opportunity for the reestablishment of conventional agriculture serving domestic markets.

Clearly any such effort must be accompanied by a vigorous interdiction program aimed at processors and transporters of coca paste. It is far more efficient to attack the drug trade at the level of the professional drug cartels than to declare war on the entire peasant population of the producing areas. JULIO E. GIANELLA Lima, Peru