In this paper, we suggest to use wavelet packet bases as an alternative to the widely used principal component analysis in an estimation of the functional autoregressive processes. By extending the notion of the socalled nonstandard form of operators representation, we search for the "best" basis on a criterion of highest correlation between pairs of wavelet packet coefficients.KEY WORDS:autoregressive Hilbertian process, functional data analysis, wavelet packet bases,ill-posed inverse problem.