LEGENDARY anchorman Walter Cronkite is being pushed round town in a wheelchair, propelled by his girlfriend Joanna Simon, sister of Carly. But there's no emergency; a spokeswoman says Cronkite, 89, has been ordered to rest while he waits for a skin graft to heal on the back of his leg, following an operation to fix an Achilles tendon he injured several years ago playing tennis. The indomitable newsman will be in Vienna in the new year for WNET's annual "Great Performances" spectacular regardless.