NEW ORLEANS-Archbishop Alfred Hughes’ decision in April to close 33 of what were once about 142 parishes in the Archdiocese of New Orleans was not only a concession to the damage wrought by Hurricane Katrina. It also introduced New Orleans Catholics to a phenomenon communities in other parts of the country began seeing two decades ago. Middle-class Catholics’ migration to the suburbs and the shortage of priests long ago began forcing bishops elsewhere to close, merge or cluster churches and parishes, sometimes to public outcry that has strained relations between lay Catholics and the church’s institutional hierarchy. In some places, critics insist there is more than demographics and personnel in the mix: They allege that bishops sometimes close financially vibrant parishes to sell off property to cover sex-abuse settlements or general operating losses. The phenomenon now is so advanced that dioceses have acquired a good deal of experience developing new ways to manage parish life.