  We analyze the decay B0-->K+ pi- pi0 with a sample of 454 million B Bbar
events collected by the BaBar detector at the PEP-II asymmetric-energy B
factory at SLAC, and extract the complex amplitudes of seven interfering
resonances over the Dalitz plot. These results are combined with amplitudes
measured in B0-->K_S pi+ pi- decays to construct isospin amplitudes from
B0-->K* pi and B0-->rho K decays. We measure the phase of the isospin amplitude
Phi_3/2, useful in constraining the CKM unitarity triangle angle gamma and
evaluate a CP rate asymmetry sum rule sensitive to the presence of new physics
operators. We measure direct CP violation in B0-->K*+ pi- decays at the level
of 3 sigma when measurements from both B0-->K+ pi- pi0 and B0-->K_S pi+ pi-
decays are combined.
