La direttiva sarebbe stata attuata in "via amministrativa" = The directive would have been implemented "administratively"; or: The directive would have been implemented "through administrative means" -- as opposed, for example, to being implemented legislatively, by vote of the National Assembly, etc. If the quotation marks around "via amministrativa" appear in the original text, then the writer apparently has some doubts or reservations regarding this procedure. -- Hope this helps!

Traduzione di tutta la frase: The directive would be carried out through administrative channels.

Uso "would be" e non "would have been" perché in Inglese basta questo per tradurre il tempo in italiano anche se non sembrerebbe. E' molto più semplice e scorrevole. Spero di essserti stata d'aiuto
Ciao
Audrey