OP; Recommend have a shop re-ream the socket in both the top and bottom of the headtube with the proper tool, face both ends while there, and then reinstall the headset. I have seen several headtubes cracked when the headset was pressed in without properly reaming of the headtube to fit the headset, as others have noted. Agree also with the other suggestion that if the bottom end is not cracked you can continue to use it with adequate safety despite a minor crack at the top. That is a good thing as repairing a cracked headtube would be quite expensive.
/K