The three girls walk into the store, and it seems that their sexuality asserts power in the way that they turn heads and capture the attention of the store-goers and employees. The girls are aware that others are watching them, but they act oblivious, and this dynamic seems to lend the girls a kind of unspoken power. However, this power proves to be something of an illusion, since the girls can't really harness it—as Sammy says, "Poor kids, I began to feel sorry for them, they couldn't help it"—and they can't adequately come to their own defense when Lengel asserts his own personal power within the store and shames them. He accuses the girls of being indecent, and in doing so asserts that the girls' attire goes against social norms, that the girls' sexuality is itself inherently indecent, and blames the girls for the men's sexual desire for them.
Sammy's response to defend the girls and sacrifice himself arises because he's both attracted to them and wants to be their defender. As he attempts to protect the girls from Lengel's power, however, Sammy actually objectifies them further in some sense—he renders them more helpless, as passive objects of desire who require his defense and can't act for themselves.
Sex, Gender, Power ThemeTracker
Sex, Gender, Power Quotes in A&P
You never know for sure how girls' minds work (do you really think it's a mind in there or just a little buzz like a bee in a glass jar?) but you got the idea she had talked the other two into coming in here with her, and now she was showing them how to do it, walk slow and hold yourself straight.
She must have felt in the corner of her eye me and over my shoulder Stokesie in the second slot watching, but she didn't tip. Not this queen. She kept her eyes moving across the racks, and stopped, and turned so slow it made my stomach rub the inside of my apron…
I bet you could set off dynamite in an A & P and the people would by and large keep reaching and checking oatmeal off their lists and muttering "Let me see, there was a third thing, began with A, asparagus, no, ah, yes, applesauce!" or whatever it is they do mutter. But there was no doubt, this jiggled them. A few house-slaves in pin curlers even looked around after pushing their carts past to make sure what they had seen was correct.
"Oh Daddy," Stokesie said beside me. "I feel so faint."
All that was left for us to see was old McMahon patting his mouth and looking after them sizing up their joints. Poor kids, I began to feel sorry for them, they couldn't help it.