There are conflicting opinions as to whether narrower tires necessarily have less rolling resistance. There was a fairly enthusiastic discussion on this subject here: http://www.bikeforums.net/touring/97...d-touring.html
which also contained links to some empirical evidence that the opposite is true. The upshot seemed to be, on balance, that more supple tires (more threads per inch) are generally lighter for a given width and have less rolling resistance, but are more susceptible to flats. Slick tires have less rolling resistance than knobby and treaded tires having wide gaps between treads. Narrow tires are generally inflated to a higher pressure than wider tires, and higher pressure yields less rolling resistance. You may have a need for wider tires which narrow tires will not fill. It is a complicated problem, and your results may vary.