RENORMALON CONTRIBUTIONS TO DELTA-P

Leading QCD vacuum polarization contributions to the electroweak param eter Delta rho are evaluated numerically using several different presc riptions for the gluon self-energy. Simple theoretical estimates of th e asymptotic behavior are given. The results show a significant contri bution from the leading infrared renormalons when Delta rho is express ed in terms of the top-quark pole mass and its absence when the MS run ning mass is employed. The calculations are applied to estimate higher -order QCD contributions to Delta rho.