WASHINGTON—The Obama administration on Monday issued a new order banning most new deepwater-drilling activities until Nov. 30, setting up a fresh round of conflict with the oil industry over when it will be safe to drill again offshore.

The latest round in the clash over the ban on new drilling got under way as BP installed a new cap on its blown-out undersea well that company and government officials hope will capture all the spewing oil. BP officials have said they are also aiming to finish drilling a relief well that will...