Like the little train that thought it could in the children’s story, a bargain-basement spacecraft no bigger than a bicycle wheel is poised to land on Mars Christmas Day and begin the first direct search for extraterrestrial life there in almost 30 years. The lander, conceived and built in Britain, is already a scientific success story for packing the most precise detection gear ever to reach the Red Planet into the smallest package. Beagle 2 has also captured the public imagination here in a grassroots way that the slick NASA publicity machine has seldom managed in the United States.