As plans for a new school in Bradford take shape, voters will likely be asked early next year to approve a debt exclusion — temporary property tax hike — to fund the project. The new school would replace the aging Caleb Dustin Hunking Middle School, a portion of which was closed in October 2011 over fears that the building’s north wing could collapse. More than 400 heavy-duty steel support columns were installed last summer to shore up the building. The fix is expected to keep the school safe for at least five years, enough time, city officials hope, to build a new school. According to Superintendent James F. Scully, the new school is expected to cost $55 to $62 million, with the Massachusetts School Building Authority covering much of the cost. City taxpayers will likely be asked to shoulder between $10 million to $15 million for the project, he said. Before voters go to the polls, officials have said they will provide information about how the temporary increase would affect homeowners’ tax bills.