In this paper we present a theoretical study of the autoionization dynamics of high (2)P(1/2)np’[3/2](1) Rydbergs (with the principal quantum numbers n = 100-280) of Ar in weak homogeneous electric fields (F = 0.01-1.0 V/cm), which were experimentally interrogated by time-resolved zero-electron kinetic energy (ZEKE) spectroscopy [M. Muhlpfordt and U. Even, J. Chem. Phys. 103, 4427 (1995)], and which exhibit a marked dilution (i.e., similar to 2 orders of magnitude lengthening) of the lifetimes relative to those inferred on the basis of the n(3) scaling law for the spectral linewidths of the np’ (n = 12-24) Rydbergs. The multichannel effective Hamiltonian (H-eff) with several doorway state(s) (for excitation and decay) and pure escape states (for decay) was advanced and utilized to treat the dynamics of the mixed Stark manifold of the ZEKE Rydbergs. H-eff of dimension 2n-1 is then constructed for a n Rydberg manifold using independent experimental information on the (l dependent) quantum defects delta(l) and the (l, K, J dependent) decay widths, which are of the form Gamma(0)(lKJ)/(n - delta(1))(3) with Gamma(0)(lKJ) being the decay widths constants. Here, l, K, and J are the azimuthal, the electronic and the total electronic angular momentum quantum numbers, respectively.