Thank you for replying.
I`m just the beginner in modeling, and I can don`t know some terms, and now I don`t know / understand what is the " the world/local icon for the tool when you extrude", what do you mean?
I have deleted the history and don`t grab other faces.
I`ll show you the sequence of my operations:
I have select neccessary Faces, then apply Duplicate operation,
then Delete the history, then Smoothing, then Delete unneccessary Faces on the new Shape, and then apply Extrude.