I'd like to correct a wrong impression that may have been conveyed by the article on the Peace Corps {front page, Aug. 2}. In it, Blaine Harden noted that the Worldwatch Institute held up the Peace Corps as a model for other developed countries and proposed a multinational assistance corps funded by the World Bank.

Such an organization already exists and has been providing volunteer technical assistance for more than 16 years. The United Nations Volunteers program currently has well over 1,000 volunteers from 80 nations serving in 91 countries.

While the Peace Corps may be a model in some respects, UNV has always filled the need of developing countries for highly technical expertise and experienced, and hence older, volunteers. It was established in part to give countries without their own Peace Corps-like groups the opportunity to serve the cause of development. Not surprisingly, volunteers from developing countries (76 percent of the total) are often more capable of adapting their skills to their countries of assignment.

In Botswana, UNV is the third largest volunteer organization (with 50 volunteers) after the Peace Corps (with 200) and the Organization of Netherlands Volunteers (with 53). It is providing doctors, computer specialists, educators, cartographers and agricultural specialists, to name a few.

A UNV chemical engineer from Nepal was responsible for the design and implementation of Botswana's first cement production plant, which uses local raw materials, provides village employment and lessens dependence on imports from South Africa. A British landscape architect has been given chief credit by local authorities for fostering creation of public parks and playgrounds in one of Botswana's principal towns. These are just two of the thousands who have made similar contributions.

While the Peace Corps is doubling in size, the UNV could potentially increase its numbers tenfold were the developed countries, including the United States, to increase their financial contributions to an organization that truly embodies the spirit of international volunteerism. CURT TARNOFF Washington The writer was country director for UNV in Botswan