It did launch with the 2.4-meter mirror.
Sat Apr 02 2011 21:28:
Another bit from New Cosmic Horizons: Space Astronomy from the V2 to the Hubble Space Telescope, this time about the Hubble Space Telescope itself (née the Large Space Telescope):
[F]urther budgetary problems forced NASA to reduce the mirror diameter
of the LST from 3.0 m to 2.4 m, saving an estimated $61m in 1975
dollars. Later in 1975 the Large Space Telescope's name was changed to
Space Telescope, so as to avoid giving Congress and the tax payers the
impression that NASA were being greedy in asking for anything 'large'
during a time of financial stringency in the USA. Some astronomers
were concerned that this change in name signaled that NASA were
eventually going to cut its diameter even more to 1.8 m, which George
Low, NASA's deputy administrator, assured them was not the case.
