25 CFR §23.43

1. (a)Tribal government programs. The appropriate Agency Superintendent or Regional Director may approve a grant application and its subsequent execution under subpart C when the intent, purpose and scope of the application pertains solely to reservations located within the service area jurisdiction of the agency or area office.
2. (b)Off-reservation programs. The appropriate Regional Director may approve a grant application and its subsequent execution under subpart D when the intent, purpose and scope of the grant proposal pertains to off-reservation Indian service populations or programs.