Probably not from within Publisher. And not with retaining the same
proportions of page size or content.

if you needed to do this simply for the purpose of proof reading, you could
make PDF from the 11x17 and then export from acrobat each spread as an eps,
then bring each eps into a new Pub file and resize as needed. Content would
likely get squished one way or another and that 10 point type is going to be
a heck of a lot smaller...etc.

--
Mac Townsend,
Adcom Graphics, Fairfield, California:
Electronic Prepress & Large Format Imaging
www.adcomgraphics.com