  We report the measurement of an inclusive partial branching fraction for
charmless semileptonic B decay and the extraction of |V_{ub}|. Candidates for
B-> X_u l nu are identified using a novel X_u-reconstruction method with
simultaneous requirements on the hadronic recoil mass (M_X) and the invariant
mass squared of lepton-neutrino system (q^2). Based on 86.9 fb^{-1} of data
taken with the Belle detector, we obtain Delta{B}(B->X_u l nu ; M_X<1.7GeV,
q^2>8.0GeV^2) = (7.37 +- 0.89(stat.) +- 1.12(syst.) +- 0.55(b ->c) +-
0.24(b->u)) x 10^{-4} and determine |V_{ub}| = (4.66 +- 0.28(stat.) +-
0.35(syst.) +- 0.17(b->c) +- 0.08(b->u) +- 0.58(theory)) x 10^{-3}.
