Does USD(AT&S) "have" or "not have" delegated authority to authorize forms of international agreements for security assistance programs?
Note: Sorry for the delay in responding. This question just reached me last week.
The forms of international acquisition cooperation you mention in your question above -- Cooperative RDT&E, Cooperative or reciprocal logistics support, and RDT&E information exchange -- are all based on various Title 10 USC legal authorities established by Congress and the President over the years. These legal authorities empower the Secretary of Defense (or his/her designees) to authorize DoD personnel to enter into international agreements or arrangements in these particular areas, subject to interagency coordination in specific circumstances. For future reference, these forms of international acquisition cooperation are generally referred to as "International Cooperative Programs (ICPs). USD(A&S) has been delegated the responsibility for ICP establishment and management by the SecDef.
U.S. Government Security Assistance programs -- the most well-know being Foreign Military Sales -- are authorized by Title 22 USC legal authorities. In most instances, the Security Assistance program legal authorities in Title 22 USC are the overall responsiblity of the Secretary of State, with substantial participation and assistance by the Department of Defense. As a result, DoD does not have unilateral authority to enter into Security Assistance program international agreements or arrangements. USD(Policy) -- assisted by the Defense Security Cooperation Agency (which reports to USD(P) -- has been delegated the responsibility by SecDef for Security Assistance program management activities within DoD (not USD(A&S)).