[texhax] equal width tabular columns when using a long multicolumn heading

[jtzzaa11-texhax1 at yahoo.com]

Hello,

I have a tabular with several columns preceded by a heading in a multicolumn. However, the heading is wider than the combined width of the columns, which results in the columns having different widths. Here is a minimal example:

\begin{tabular}{ c c c }
\multicolumn{3}{c}{long heading}    \\    
1 & 2 & 3\\
\end{tabular}


which results in 


long heading
1 2         3


so the last column is much wider than the first two.
Is there a way to automatically generate equal width columns whose combined width equals the width of the long heading?. I am trying to avoid manually fixing the width of the columns, for example, using p{2cm}.


Thanks,
Joel.