Your terminology is a bit confused; A. is a stem, A.I is a compound symbol (or compound variable).
No, the COMPARE function cannot be used on stems, only on strings (which compound symbols resolve to). Having parsed the lines into stems, IMNSHO your best bet would be to compare them in a loop i = 1 to alarm.0 (remember that, although storing the nuber of assigned variables in stem.0 is a common convention, it is only a convention, and Rexx will not automatically do it for you). Do not forget to handle crossings of the midnight boundary.
"You have sat too long for any good you have been doing lately ... Depart, I say; and let us have done with you. In the name of God, go!" -- what I say to a junior programmer at least once a day