I forgot to write that C-g in emacs does not produce any effect, I have to kill it, and the processes are in these states:
10985 pts/1 R 12:09 _ emacs 10986 ? S 0:00 _ /usr/local/libexec/emacs/21.3/i686-pc-linux-gnu/emacsserve 11004 pts/4 S 0:11 _ /local/languages/clisp//lib/clisp/full/lisp.run -B /local/
Just for the record, the problem was a bug in my .emacs which redefined with a bug the string function. Without my bug, there's no problem with slime/clisp.