COMPLETE TREE LEVEL CALCULATION OF THE PROCESS E--]NU(NU)OVER-BAR-B(B)OVER-BAR AND THE HIGGS SIGNAL AT LEP200 AND NEXT LINEAR COLLIDERS(E)

We present the results of a complete tree level calculation for the pr ocess e+e- --> nunubbBAR at the energies of LEP200 and Next Linear Col liders. Automatic generation of the squared matrix element was carried out by GRACE and CompHEP systems. We study in detail the behavior of the cross-section as a function of CMS energy and Higgs boson mass. Pa rticularly we point out the possibility of Higgs boson detection at LE P200 energies under the resonance threshold (square-root s < m(H) + m( Z)). We compare the complete tree level result with the effective 2 -- > 2 process approximation for Higgs production. The approximation is s atisfactory at LEP200 energies, but at higher energies a rather large discrepancy is observed.