[fptex] MetaPost question

[Jose Carlos Oliveira Santos]

Hi,

I would like to know what should I do in order to use LaTeX instead of TeX
to process text in a MetaPost job. According to the file Mpost.dvi (it is
located at \texmf\doc\manpages):

"Here is a list of the environment variables affect of the behaviour of
mp:

[...]

TEX  The version of TEX - or LATEX - to use when processing btex and
     verbatimtex commands. Default tex. This version of MetaPost allows
     you to use a `%&format' line instead.""

How do change the TeX variable under fptex?

Best regards

Jose Carlos Santos