The CBS News anchor was among 4 women tapped to appear on different covers of an upcoming SI issue -- and she's kinda the odd woman out, since the others are veteran models in the biz ... including Chrissy Teigen, Hunter McGrady and Kate Upton.

All those gals are also a lot younger than Gayle, which makes her shoot all the more eye-popping. Frankly, she looks incredible in her spread ... rocking several different bathing suits.

GK models several different styles here ... all of which are tasteful and suit her quite well. Of course, with her trotting out all the different swimsuits -- she's also putting her figure on display, and it's safe to say ... Gayle's still got it, as she's absolutely gorgeous in the pics.

Now, in terms of how Gayle feels about the attention ... she's actually pretty bashful about it all. GK was on her show "CBS Mornings" Tuesday talking about it, and she says she was stunned to have been asked to participate ... explaining she didn't think she was worthy.

Drew Barrymore and the rest of the anchors assured her she 100% was ... noting she looks great, and that her inclusion probably does a lot more good than she might realize.

As you may know ... SI and other magazines like it have made an effort in recent years to get different types of people featured for their shoots -- and it's sparked a robust conversation about representation as well as beauty standards, which are being redefined every day.