A community development plan may be modified from time to time by resolution of the legislative body, provided, where the proposed modification substantially changes the community development plan, no such modification may be adopted until such modification is referred to the planning agency of the municipality. If the modification contemplates activities which affect a housing authority or the modification contemplates activities within a development project area, harbor improvement project area, housing site development project area, redevelopment or urban renewal project area, or if the modification contemplates human resource development activities, the modification shall likewise be simultaneously referred to the housing authority, the economic development agency, the harbor improvement agency, the housing site development agency, the human resources development agency or the development agency, as the case may be, for review and comment on the portion of the modification falling within the jurisdiction of the particular authority or agency. The agency shall submit written comments to the legislative body not more than two weeks after receipt of the plan by such agency. Failure of the agency to comment within fifteen days shall be deemed approval of such plan. Prior to the approval of the modification, the legislative body shall hold at least one public hearing on the modification, notice of which shall be not less than two weeks prior to such hearing.