Many of those who testified before Congress in the Iran-contra hearings remarked that that body should not have had such an inconsistent policy on aid to the Nicaraguan rebels. In an op-ed article July 28, Henry Kissinger stated that "Congress has an obligation to put forward a clear-cut expression of what it desires."

These people are plainly wrong. The judicial branch has an obligation to follow precedent, thus maintaining relatively consistent policies, but the legislative branch has no such duty. Our political system is structured so that the public can use it to modify government policies by changing its representation. That is what happened to contra aid. Last summer, Congress reversed the Boland Amendment by a narrow margin in both Houses, as a result of changes in membership and public opinion. By doing so, the members instituted a new, clear policy.

However, there was also a clear policy at the time U.S. dollars were diverted to the contras, contrary to what Mr. Kissinger would have us believe. Then such a diversion was strictly forbidden by the Boland Amendment. SHAWN NOLAN Philadelphia

I enjoyed reading the article by Henry Kissinger. He has made, as usual, the best summary of the long hours and tons of paper that have come out as a result of the congressional hearings on the matter.

However, and with due respect to Mr. Kissinger's expertise, I would dare to suggest that there is another fundamental flaw in the approach of the Reagan administration to the Nicaraguan problem. Mr. Kissinger states that "the fundamental mistake made by the administration was to seek to achieve by indirection what it should have faced head on." I understand this to mean that the administration should have sought some kind of popular support for the measures taken against Nicaragua before carrying them out.

And what about the support of the other members of the OAS system? After all, Nicaragua is not a possession or a territory of the United States. The Sandinista regime is recognized by all the members of the Organization of American States -- including the United States -- and is also a member of the United Nations.

Mr. Kissinger says a second choice for the United States regarding Nicaragua is "to bring pressure on Nicaragua to return to the inter-American system," etc. But Nicaragua has not been found guilty by the OAS of any violation of its duties and obligations under either the OAS charter or the Rio Treaty. By ignoring the two basic instruments of the inter-American system, the United States has failed to establish a legal and credible basis to seek the overthrow of the regime in Nicaragua.