Federal Reserve officials are close to deciding they will maintain a larger portfolio of Treasury securities than they’d expected when they began shrinking those holdings two years ago, putting an end to the central bank’s portfolio wind-down closer into sight.

Officials are still resolving details of their strategy and how to communicate it to the public, according to their recent public comments and interviews. With interest rate increases on hold for now, planning for the bond portfolio could take center stage at a two-day...