Zak,

The best way to maintain as much strengh and mass when trying to drop weight is to cut carbs and keep protein and fat intake at relatively high levels. The quality and quantity and quality of the protein you eat will also be more important during periods of weight loss.
A ketogenic diet(no - very low carbs during the week, weekend carb-up) will typically help you maintain the largest amount of strength and mass during calorie restriction.

Good Luck,
Danny