κλύοις ἂν, a reverent petition; cp. 1491.
προστατήριε: see on Tr. 208 f. “τὸν εὐφαρέτραν” | “Ἀπόλλω προστάταν”. Like Artemis ( Aesch. Th. 449), Apollo was thus called as ‘defender’ of the house before which his image or altar stood. Here Clytaemnestra is invoking him more especially as “ἀλεξίκακος”, averter of evil: Ar. Av. 61“Ἄπολλον ἀποτρόπαιε”.