Create a placeholder graphic frame on the master page for your document. Select the placeholder frame and choose Object > Fitting > Frame Fitting Options. Assuming your placeholder frame is the same proportions as the 24 x 36 page size, select the Fitting menu to choose Fill Frame Proportionally.
As you place the PDF, when you place each PDF page as a graphic, it should scale to the placeholder frame size.
For this sort of thing I really like Scott Zanelli's multipage importer script. It allows you to specify position and scale, and will do the whole set at once. See InDesignSecrets » Blog Archive » Zanelli Releases MultiPageImporter for Importing both PDF and INDD Files
As usual, 100% agree with Peter. I use multipageimporter all the time and swear by it.
There is a recent script that is handy when there are multiple files in a directory that need to be scaled to fit a page, and is starting to become a favorite. http://www.rolanddreger.net/index.php?id=310
Downloaded the script and will try it out. I do see it's for CS5 but should work.