Nuclear treaty between US-USSR mentioned by Grusch – FOIA followup

Hello all. I have been lurking so far, but recently I decided to take more active stance. Since the Congress hearing I can’t stop thinking about hint Grusch made about the 1971 “Agreement on Measures to Reduce the Risk of Outbreak of Nuclear War Between The USA and The USSR”.

Now-declassified update to that agreement dated 1976 here:
https://nsarchive.gwu.edu/document/27622-document-3-secretary-defense-assistant-president-national-security-affairs

This is part of a cache of declassified documents describing the history of false nuclear alarms –
https://nsarchive.gwu.edu/briefing-book/nuclear-vault/2022-03-24/colonel-odoms-chilling-four-am-phone-call

The 1976 memo describes six “Situations” that could trigger emergency communication with the Soviets in order to avoid nuclear escalation. Of special importance to UAPs is the Situation Two:

“b. Situation Two: Detection by missile warning system of unidentified
objects, if such occurrence could create a risk of outbreak of nuclear
war between the USA and the USSR.

Short message to be transmitted: ATOM 222″

Now I want to dig deeper and follow up with some FOIA – do you have any suggestions as to which agencies should I target? I have no previous FOIA experience.

I already started sending some requests, DIA and Dept of State, but its groping in the dark. Any useful info would be much appreciated.