Many thanks to Blaine Harden for the Aug. 2 article portraying the strengths of the modern Peace Corps. Recognition of the steady, effective service to grass-roots development by Peace Corps volunteers is long overdue. So is recognition of Loret Miller Ruppe's six-year, inspired stewardship of the tiny agency. She has given President Kennedy's creation bipartisan colors.

However, Mr. Harden's characterization of Peace Corps volunteers of the 1960s as ''unskilled idealists'' is highly inaccurate. Idealists, yes. It is, after all, first and foremost a corps dedicated to peace, and not a miniature World Bank or Agency for International Development. Unskilled, no. It is well documented that many thousands of early volunteers serving in Africa as teachers made enormously valuable contributions to the expansion and improvement of public schools in more than 20 African countries. Similar contributions were made in public health and other fields. Africans will tell you so.

The early volunteers were tough too. Quitting before completing two years of service was below 10 percent in the '60s, compared with today's 25 percent. Finally, while the average age of volunteers today is 30, the majority are still young people.

It is past due for today's Peace Corps to step out of the shadow of the bold experiment of Sargent Shriver's years as director, but this does not have to be done by casting false aspersions on the volunteers of the '60s. The fact is that the many achievements of the Peace Corps have been remarkably continuous. And the majority of volunteers then and now have been pragmatic idealists serving with distinction. ROGER LANDRUM President Returned Peace Corps Volunteers of Washington, D.C. Washington