index{index entry arabic{counter}}

"index entry arabic{counter}"

"index entry 1".

documentclass{article}
%usepackage{makeidx}% using this, "arabic{section}" expands to 1, 2, 3,...
usepackage{index}% using this, "arabic{section}" does not expand
makeindex
newcommand*{Index}[1]{index{#1}}
begin{document}
section{First  Section} Index{first  arabic{section}}
section{Second Section} Index{second arabic{section}}
section{Third  Section} Index{third  arabic{section}}
section{Fourth Section} mbox{index{fourth arabic{section}}}
section{Fifth  Section} mbox{index{fifth  arabic{section}}}
section{Sixth  Section} mbox{index{sixth  arabic{section}}}
printindex
end{document}

indexentry{first 1}{1}
    indexentry{second 2}{1}
    indexentry{third 3}{1}
    indexentry{fourth 4}{1}
    indexentry{fifth 5}{1}
    indexentry{sixth 6}{1}

indexentry {first arabic {section}}{1}
    indexentry {second arabic {section}}{1}
    indexentry {third arabic {section}}{1}
    indexentry {fourth arabic {section}}{1}
    indexentry {fifth arabic {section}}{1}
    indexentry {sixth arabic {section}}{1}

Dan