The International Trade Commission ruled the South Korean company's mobile devices infringed on two Apple patents -- one for multi-touch graphical user interface and another that detects when a set of headphones is removed from its phone socket.
The multi-touch GUI refers to the touchscreen's ability to recognize the presence of two or more points of contact with the surface. This plural-point awareness is often used to implement advanced functionality such as pinch to zoom or activating predefined programs.
But the ITC rejected other Apple claims and said Samsung didn't violate four other Apple patents.
In its ruling, the ITC overturned an administrative judge's earlier conclusion Samsung infringed on a design patent covering rectangular smartphones with rounded corners.
The trade body said Samsung could still import and sell its infringing devices while the Obama administration reviews the order over the next 60 days.
The Obama administration last week vetoed a June ITC order that said Apple had violated a Samsung patent. The vetoed order would have barred the sale of some older-model, AT&T-specific iPhone smartphones and iPad tablets.
After last week's veto, the South Korean government said it would closely monitor Friday's ITC ruling.
The government and Samsung had no immediate comment on the ruling, which was issued in Washington Friday afternoon.
Apple said: "With today's decision, the ITC has joined courts around the world in Japan, Korea, Germany, Netherlands and California by standing up for innovation and rejecting Samsung's blatant copying of Apple's products. Protecting real innovation is what the patent system should be about."