Consider this scenario. Your Contracting Officer tells you that he is too busy to manage your specific contract and suggests that, instead of calling him, you should speak to and get guidance from the assigned Contract Specialist about any problems that you may have under the contract. Can you rely upon the directions and guidance that you receive from the contract specialist; especially if the direction you are given may cause you to incur additional costs?
My advice is to be very careful in this situation. Although not common in the federal contracting sector, some Contracting Specialists do possess a certain amount of warrant authority. I always remind my students to review Section G of their contract when trying to determine who has authority to contractually bind the Government. In that regard, and as a general rule, it often only identifies one person — the Contracting Officer. The contract may, in some circumstance, identify more than one (as you have suggested) with a further description of limitations of authority (e.g., dollar thresholds). In this particular situation, I would memorialize your conversation in an email back to the CO so that his instruction to you is in writing. I also suggest that any future correspondence that you may have with the contract specialist be also sent to the Contracting Officer (either directly or as a “cc”) so that he/she has actual knowledge of the guidance/instructions given. Although not “foolproof”, taking these steps should help you in the event questions with regard to reimbursement of costs or a dispute arise in the future.