\newcounter{parnum}
\newcommand{\N}{%
\noindent\refstepcounter{parnum}%
\makebox[\parindent][l]{\textbf{\arabic{parnum}.}}}
% Use a generous paragraph indent so numbers can be fit inside the
% indentation space.
\setlength{\parindent}{2em}
se pone antes del párrafo \NTomado de http://garoth.com/?p=48
\makeatletter
\renewcommand\l@section[2]{%
\ifnum \c@tocdepth >\z@
\addpenalty\@secpenalty
\addvspace{1.0em \@plus\p@}%
\setlength\@tempdima{1.5em}%
\begingroup
\parindent \z@ \rightskip \@pnumwidth
\parfillskip -\@pnumwidth
\leavevmode \bfseries
\advance\leftskip\@tempdima
\hskip -\leftskip
#1\nobreak\
\leaders\hbox{$\m@th\mkern \@dotsep mu\hbox{.}\mkern \@dotsep mu$}
\hfil \nobreak\hb@xt@\@pnumwidth{\hss #2}\par
\endgroup
\fi}
\makeatother