Must a CO sign an Interagency Agreement?

A warranted contracting officer obligates funding - even if that funding is being obligated between agencies. See OMB Guidance dated June 2008 regardig Interagency Acquisitions. If you are in the DoD, please see the DoD Financial Management Regulation 7000.14R, 11a_03 and DoD Instruction 4000-19 dated 9 Aug 95. Also, see FAR Part 17.504(d)(3) - statutory authority for contractual actions - a contracting officer has statutory authority up to their warrant amount. If you are interested more in IAs, send me an e-mail separately and I can send you what I have.

Interagency agreement about what?

IA is for information services our agency is providing to the requesting agency under IDIQ contract we have with a vendor. The requesting agency does not have a CO sign off on their IA, only funding official. This is a non-Economcy Act IA. We are using revolving fund authority.

So the IA is pursuant to FAR 17.502-1(?

Yes. The IA is signed, but just not by a warranted CO.

I know of no statutory or regulatory requirement that a CO sign the IA.

I agree. I've looked at this for years and the answer always is the same - there's no requirement for a CO to sign.