Trump Wanted To Get Look at Young Aide's Butt, Ex-WH Press Sec. Claims

"Let’s bring her up here and look at her ass."

That's what former President Donald Trump told staffers as he summoned a "young, highly attractive" aide to his private office on Air Force One ... this according to a new book.

Stephanie Grisham -- the former White House press secretary under Trump famous for holding zero press briefings -- makes the claims in her book due out Tuesday, saying she tried to keep Trump away from the press wrangler he allegedly took a liking to.

TMZ's obtained an excerpt from the book -- titled "I'll Take Your Questions Now: What I Saw in the Trump White House" -- in which Grisham says Trump was ogling the young woman from the day he first laid eyes on her.

In fact, Grisham writes ... "I began to notice that he was taking an unusual interest in a young, highly attractive press wrangler on my team ... What I do know is that he behaved inappropriately. And, since the woman worked for me, I tried to protect her and keep his unusual interest in her under wraps."

Grisham says Trump often asked her about the woman, and when he wanted the aide to see him on Air Force One, Grisham made sure they weren't left alone because, "the whole thing never felt quite right."

Things allegedly got weird on one trip Grisham missed ... she claims Trump asked how the woman was doing before instructing his staff to bring her to his office cabin so he could get a look at her butt ... so Grisham tried keeping the aide off future trips.

Grisham says she doesn't know if anything happened between Trump and the woman, but she writes that she came close to telling Melania about her husband's alleged behavior before ultimately being "too chickens***."