The amplitude of diffractive ρ (and open quark) leptoproduction on a
polarized target is calculated in the leading log approximation of pQCD using
the hadron-parton duality hypothesis. The spin-spin asymmetry is expressed in
terms of the spin dependent gluon and quark structure functions in the small
x region. Therefore the γ∗+p→ρ+p reaction provides a promising
tool to study the spin dependent gluon distribution ΔG(x,q2).Comment: 13 pages, LaTeX, 2 figure