Solar Warden by Peter Fuller

Earth is in peril. The reptilians and grays, led by their Blue Nordic overlords, have suffered a series of humiliating defeats at the hands of the humans–a species they deem inferior. Retaliation is inevitable. Expecting a divide-and-conquer strategy by the aliens, Solar Warden begins reinforcing its Mars Base–the enemy's expected target. And the final stepping stone to earth. In the midst of the impending invasion, Steve "Scarecrow" Richardson and his new love, Major Sandy Cooper, are marked for death by both human and alien threats.