overflow-y how solve this

overflow-y how solve this

I have a div, with width 972px, but I have two pages, when one page have a
height of 1000px+ and other have height 800px+-.
look:
HTML
<div id="wraper">
</div>
CSS:
#wraper { width: 978px; margin: 25px auto; }
the height is two pages are diferent, one is 1000px+ (the scroll is
active), and other is 800px (the scroll isn't active).
The problem is, why solve this problem, maintaining centralized
independent div scroll appear or not? How to scroll the viewport
ignored.