The Post's editorial "Salesmen in Uniform" (Aug. 13) is misleading. It imputes to me a senseless encouragement of weapons sales by the Department of Defense, citing my directive to the military services. I would like to set the record straight.

First, U.S. military personnel are not instructed to tell foreign governments to procure the FX aircraft. When we deal with foreign governments, we deal with sovereign nations that must commit their own resources to purchase military equipment. We have numerous limitations on what we will sell, to whom and under what circumstances. We do encourage U.S. military personnel to consult and, where appropriate, suggest that one weapon system may be more suitable than another. This is not "peddling" U.S. arms or supplanting U.S. private contractors. It is "offering" quality advice that will assist friendly governments to plan wisely and to utilize their resources in the most cost-effective way. Our friends should expect nothing less from the United States.

The Post editorial appears to miss the point of my decision. It was not intended to favor one company over another or blur the distinction between "military responsibilities and commercial favors for private companies," as the newspaper alleges. Quite the contrary. It is intended to reinforce what has been U.S. policy since the FX program was given a green light by the Carter administration: to ensure that all candidate aircraft receive evenhanded treatment.

Next, the editorial implies it is not appropriate for U.S. military representatives to engage in planning efforts that could result in a more informed procurement decision by our friends or allies. I hardly see how it serves our interests to tand idly by while our allies invest their limited resources in programs that are either too ambitious or too costly for their particular needs.

If one starts from the assumption that these countries have valid defense requirements, then it is only logical that the United States should encourage decisions that respond appropriately to the threat and hold costs down. The FX gives responsible political and military leaders an alternative to the highly sophisticated and expensive aircraft that are sometimes all too attractive.

Finally, the editorial alleges that this administration is "rapidly losing any sense of proportion" on the issue of foreign arms sales. The Post and other commentators frequently ignore the fact that U.S. foreign military sales in FY 1981 were the lowest in almost eight years and, when inflation is accounted for, dollar sales in this fiscal year are about the same as in 1970. Few editorials point out that most U.S. arms go to countries that pay cash and few editorials note that the overwhelming proportion of U.S. arms are purchased by the more affluent industrialized countries. Fewer still recognize that less than 40 percent of U.S. foreign militay sales involve lethal equipment or ammunition, while the remainder involve military support, services and spares.

In sum, the rising cost of military (and civilian) technology together with rising inflation have combined to price advanced U.S. fighter aircraft beyond the reach of many foreign governments. These nations that can afford to buy sophisticated aircraft and that have legitimate defense needs can, as sovereign nations, request first-line aircraft. Most other nations may, for financial reasons or particular security requirements or absorption limitations, prefer a less costly but high quality aircraft such as the FX. By making the FX a viable alternative to more advanced aircraft, the United States has made a conscious decision to respond to the legitimate self-defense needs of our friends while, at the same time, not overburdening them with extraordinary financial obligations or inappropriate technology difficult to absorb and utilize effectively.