general problems of the 2002 Subaru Impreza Wrx

Traveling on a damp, bumpy asphalt road in seattle (tempurature was in the mid-40's). Light ahead turns red - I apply the brakes as usual, but the peddle suddenly sinks about an inch and I feel abs come on. It feels as if the brakes have no stopping power and are only working at about 10%. I let up on the brakes and tried again, and was able to stop before hitting the car in front of me. This has also happened once before, on some metal drawbridge grating. It seems as if the abs comes on in times when it should not, which causes the brakes to practically not work. If a car had been closer in front of me, I would have hit it.