Final answer:
The chief of staff is responsible for advising the president about the agenda during the meeting.
Step-by-step explanation:
The officer responsible for advising the president about the agenda during the meeting is the chief of staff. The chief of staff heads and supervises the White House staff, including the president's personal staff of assistants and advisors. They are responsible for organizing and managing the president's schedule, ensuring that important topics are addressed during meetings, and providing advice and recommendations on various issues.