In the wake of the terrorism attempt Friday on a Northwest Airlines flight, federal officials on Saturday imposed new restrictions on travelers that could lengthen lines at airports and limit the ability of international passengers to move about an airplane.

The government was vague about the steps it was taking, saying that it wanted the security experience to be “unpredictable” and that passengers would not find the same measures at every airport  a prospect that may upset airlines and travelers alike.

But several airlines released detailed information about the restrictions, saying that passengers on international flights coming to the United States will apparently have to remain in their seats for the last hour of a flight without any personal items on their laps. It was not clear how often the rule would affect domestic flights.

Overseas passengers will be restricted to only one carry-on item, and domestic passengers will probably face longer security lines. That was already the case in some airports Saturday, in the United States and overseas.