\expandafter\xdef\csname c@tcode\endcsname{\the\catcode`\@}
\catcode`\@=11
%
\newdimen\leftm@rgin   \leftm@rgin=1.5in
\newdimen\rightm@rgin  \rightm@rgin=1n
\newdimen\topm@rgin    \topm@rgin=1in
\newdimen\bottomm@rgin \bottomm@rgin=1in
%
\def\leftmargin{\afterassignment\setmargins\leftm@rgin}
\def\rightmargin{\afterassignment\setmargins\rightm@rgin}
\def\topmargin{\afterassignment\setmargins\topm@rgin}
\def\bottommargin{\afterassignment\setmargins\bottomm@rgin}
%
\def\setmargins{
\dimen255=\leftm@rgin \advance\dimen255 by -1in \hoffset=\dimen255
\dimen255=8.5in \advance\dimen255 by -\rightm@rgin 
\advance\dimen255 by -\leftm@rgin \hsize=\dimen255
\dimen255=\topm@rgin \advance\dimen255 by -1in \voffset=\dimen255
\dimen255=11in \advance\dimen255 by -\bottomm@rgin 
\advance\dimen255 by -\topm@rgin \vsize=\dimen255}
%
\catcode`\@=\c@tcode
