"termcap" doesn't work

[cch]

hi all,
I use gnome-terminal whose $TERM is xterm.
when I invoke screen the $TERM is changed to "screen",
which make my "aptitude" and "mutt" etc. draw a very
dirty screen. I suppose it is because of a wrong $TERM.
When I try to change $TERMCAP by using "termcap ..." in
".screenrc", I find that that setting just doesn't
affect the $TERMCAP after I restart screen.

Can anyone help to find where the problem is ?
Thank you in advance.