tar without timestamp

Currently when I tar files I get the follow format:

-rw-r--r-- avichaiz/ftp    409 2010-11-01 17:30:58 file1.txt
-rw-r--r-- avichaiz/ftp    409 2010-11-01 17:30:58 file2.txt
-rw-r--r-- avichaiz/ftp    409 2010-11-01 17:30:58 file3.txt

This cause that when I tar the same files twice and diff the results it is not identical due to the different internal timestamp.

How I can remove the internal files timestamp or set it to known value so the archive will be always identical?

GNU tar for example can tell you which content of your archive is different to the current file system. It tells you about date, size and content differences. Based on that you could decide to update your current archive for example.

Interessting switches might be "-d [--diff, --compare]" and for updating -u [--update].