<Page>

                                                                   EX-99.906CERT

                           CERTIFICATIONS PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

Pursuant to section 906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. Section
1350), the undersigned officers of American Strategic Income Portfolio Inc. (the
"Fund") do hereby certify, to the best of each such officer's knowledge, that:

1.     The N-CSR of the Fund (the "Report") fully complies with the requirements
       of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

2.     The information contained in the Report fairly presents, in all material
       respects, the financial condition and results of the operations of the
       Fund.

By:    /s/ Thomas S. Schreier, Jr.
       ----------------------------
       Thomas S. Schreier, Jr.
       President

Date: August 6, 2004

By:    /s/ Joseph M. Ulrey III
       ----------------------------
       Joseph M. Ulrey III
       Treasurer

Date: August 6, 2004