Double expansions of the universal combination R-xi(+) of the critical
amplitudes of the singular part of the specific heat and of the corre
lation length in the homogeneous phase of the 3D and 2D dilute Ising m
odels are calculated to the fourth and third order, respectively, in p
owers of the renormalized coupling constants. The calculation is perfo
rmed within the framework of renormalized perturbation theory in fixed
dimension. Numerical estimates are obtained by the use of Pade-Borel-
Leroy approximation. The R-xi(+) estimate for the 3D case is comparabl
e in accuracy to the critical exponent values, while for the test case
of 3D Ising model it is in accordance with the exact value 1/root 2 p
i. (C) 1998 Elsevier Science B.V, All rights reserved.