Wool pants should ideally be dry cleaned by a professional. However, you can safely hand wash most wool pants in lukewarm water, being extremely careful not to shrink, stretch or otherwise alter the shape of the garment.
The risk of the pants shrinking depends on its specific blend of materials. Most wool pants are made of a bland of wool and acrylic, and are less likely to shrink than a 100% wool sweater. Still, it is easy to damage the shape and fit of wool pants by washing them in a washing machine.
To hand wash wool pants, fill a tub with lukewarm water. The water should feel comfortable to your hands. Add mild, wool-safe detergent and swirl around. You may also add 3/4 cup of white vinegar to effectively remove odors. Submerge the wool pants in the water and gently swirl around. Do not wring or rub the material as this will stretch it out and alter its fit. Pull the pants out of the water, drain the tub, and refill it with clean, lukewarm water. Submerge the pants and swirl them again. Pull them out, and gently roll them up in a clean towel to squeeze out water without wringing or rubbing. Let the pants dry on the towel, keeping in mind that wool tends to set in place as it dries.