  We theoretically investigate the interplay between charge ordering and
magnetic states in quasi-one-dimensional molecular conductors TMTTF$_2X$,
motivated by the observation of a complex variation of competing and/or
coexisting phases. We show that the ferroelectric-type charge order increases
two-dimensional antiferromagnetic spin correlation, whereas in the
one-dimensional regime two different spin-Peierls states are stabilized. By
using first-principles band calculations for the estimation for the transfer
integrals and comparing our results with the experiments, we identify the
controlling parameters in the experimental phase diagram to be not only the
interchain transfer integrals but also the amplitude of the charge order.
