Disable numbering of sub-sectioning commands under a starred sectioning command

Question

I wish to have a "Introduction" section that is not numbered, with subparts within it. I wish the subsections of that section not to be numbered, yet the whole thing to appear in the table of contents.

If I use

\section*{Introduction}
\addcontentsline{toc}{section}{Introduction}
\subsection{First part of intro}
...
\subsection{Second part of intro}

...then the \subsection commands will (in the numbering scheme I use) generate numbering such as "0.1 First part of intro" both in-text and in the TOC.

The following generates what I want:

\section*{Introduction}
\addcontentsline{toc}{section}{Introduction}
\subsection*{First part of intro}
\addcontentsline{toc}{subsection}{First part of intro}
...
\subsection*{Second part of intro}
\addcontentsline{toc}{subsection}{Second part of intro}

Is there a way to automagically do this? My problem is that I have to type the \addcontentsline everywhere, when I would like to have something where \section* triggers a switch to "non-numbered mode" where each \subsection command is expanded to the pair of \subsection*;\addcontentsline commands or something similar (and the next \section switches back to "numbered mode").

EDIT: disabling numbering of subsections for the whole document is not desired.

Answer 1

You can change secnumdepth for the introduction and afterward:

\documentclass{article}

\begin{document}
\tableofcontents
\setcounter{secnumdepth}{-1}% number only levels up to -1 (section is 1)
\section{Introduction}
\subsection{First part of intro}
\subsection{Second part of intro}
\setcounter{secnumdepth}{3}% back to default of article.cls
\section{First Section}
\subsection{First part of first section}
\subsection{Second part of first section}
\end{document}