If I recall correctly, the tank was not originally to be named after Gen. Abrams; however, I cannot recall (nor determine via Google) the original intended namesake. The closest I can determine is Gen. Westmoreland, but that doesn't sound right to me..
In "M1 Abrams: MBT 1982-1992", Stephen Zaloga notes that the original plan was to name it for George C. Marshall. They switched to Creighton Abrams as he had been an early supporter of the XM1 project. He died in 1974, at the very beginning of the development program (The taskforce to lead the project had been formed in 1972), so he never really saw it reach culmination. He was pretty well loved by the tankers apparently, and given his connection to the project, it would seem to be an appropriate way to honor him.
What I can't find in any of my books that touch on the M1 however, is discussion of why Marshall was originally chosen! I mean, it is pretty obvious on one level why he would be deserving of the honor, being the Chief of Staff during WWII, and later serving as Sec. State and Sec. Def., but I can't find anything which gives specific details on why they originally settled on him as opposed to another worthy figure. Abrams having been alive when the program started though, if they had decided on Marshall early on, presumably Abrams' name wasn't initially mentioned.