I succeded by:
1) disconnecting and turning off the iPad
2) plugged the iPad back into the computer
3) press and hold the top and home button until the iPad said to connec to iTunes
4) launched iTunes and updated, then restored the entire iPad
I THOUGHT I tried this before, but the second time I tried it on another Mac (but suspect that had nothing to do with it). I may not have held the two buttons down long enough the first time to get the message on the iPad.