During normal business hours:

Monday through Thursday
from 7:00 a.m. to 4:00 p.m.
Friday from 7:00 a.m. to 12:00 p.m.

From Guatemala: Ph. 2326-4000
From USA: Ph. 011-502-2326-4000
By e-mail AmCitsGuatemala@state.gov

After hours:

On weekends and outside normal business hours, please call the Duty Officer.  Please note that the Embassy will not be able to issue you a replacement passport outside of normal business hours.

From Guatemala: Ph. 2331-2354
From USA: Ph. 011-502-2331-2354
By e-mail AmCitsGuatemala@state.gov