If the embassy is not withholding your federal and state taxes , then you have to enter your income as if you have received a 1099-MISC.
If they withheld federal and State taxes ( most don't I think ), then you have still go to prepare Schedule-SE for self-employed taxes -- thus pretend you received a 1099-MISC but federal and state taxes had been withheld.
Does this make sense?
Which embassy ?