A B757-200 IN TOW EXPERIENCED A RWY INCURSION DUE TO INADEQUATE COM BTWN TUG DRIVER AND COCKPIT TECHNICIAN RELAYING TWR INSTRUCTIONS. TUG TWR RADIO WAS INOP.

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I WAS IN THE COCKPIT ON THE RADIO FOR A TOW FROM GATE XY TO THE HANGAR. I WAS INITIALLY TOLD TO HOLD SHORT ON TXWY A AT TXWY E. AFTER A SHORT WAIT; I WAS TOLD TO PROCEED ON TXWY E AND HOLD SHORT OF RWY 28L. I RELAYED THIS TO MY TUG DRIVER AND HE WANTED ME TO CALL THE TWR AND RECONFIRM AS THIS WAS OUT OF OUR WAY. I CALLED THE TWR AND CONFIRMED THE RTE. I RELAYED THIS TO THE TUG DRIVER. WHEN I TOOK MY THUMB OFF THE MIKE BUTTON; I THOUGHT TWR WAS CHANGING OUR RTE FROM HOLD SHORT OF RWY 28L TO CROSS RWY 28L HOLD SHORT OF RWY 28R. I REPEATED THE SUPPOSED CHANGE BACK TO TWR; THEN RELAYED IT TO THE TUG DRIVER. IF TWR WAS TELLING ME I HAD THE RTE WRONG IT COULD HAVE BEEN WHILE I HAD THE BUTTON PRESSED TALKING TO THE TUG. THE TUG WAS APPROX 20 FT ONTO RWY 28L WHEN I NOTICED THAT THE INCOMING PLANE WAS LNDG ON THE RWY. I TOLD THE TUG TO BACK UP IF THERE WAS ROOM AND HE PROCEEDED. THE TWR CALLED US WHEN WE STARTED BACK AND I TOLD THEM WE WERE BACKING UP. THE OTHER ACFT WAS TURNING OFF THE RWY AT A PREVIOUS TXWY AT THIS TIME AND TWR TOLD ME TO PROCEED ACROSS RWY 28L.