BROOKLYN - It may soon cost straphangers a bit more to refill their MetroCards as the MTA is considering another round of fare hikes. The MTA is mulling a proposal that would raise single fares from $2.25 to $2.50, and would increase weekly and monthly rates. The agency will be holding several public hearings next month, including one here in Brooklyn, to get public input on the potential hikes. The Brooklyn hearing will be held on Nov. 7 at the Marriott on Adams Street.