This specific piece of correspondence may be found on Joshua
Lederberg's NLM website, identified with the ID:
bbgcxg.
http://profiles.NLM.NIH.gov/BB/
In this piece of correspondence to Robert Jastrow, Joshua Lederberg makes it clear that biological warfare is involved in the space program, due to possible contamination of the moon and planets. However, biological warfare is of even greater importance in the case of 'back contamination'(the contamination by microbes or viruses originating from the Moon, planets, or space) because such life forms could be used in biological warfare.
In addition, we already know that Joshua Lederberg was under contract at Fort Detrick in 1951, with no evidence that he ceased working under contract at Fort Detrick. Moreover, we know that Joshua Lederberg's research at Fort Detrick involved decreasing the survivability of infected living forms. This suggests that the research Joshua Lederberg was involved in was directly related to biological warfare.
Joshua Lederberg makes it quite clear that he believes it is morally defensible to deceive people by hiding work in biological warfare at Fort Detrick.
It should also be noted that Joshua Lederberg worked with such people as Charles Philips, Riley D. Housewright and Werner Braun, all of whom worked directly with biological warfare. Indeed, Riley D. Housewright proposed the use of biological weapons in Cuba during the Cuban Missile Crisis of 1962.