Comparing the contents of .tar or .tar.gz files?

[Adam Funk <a24061@yahoo.com>]

In order to compare the contents of two archives, I've been doing
this.

$ mkdir test-foo test-bar
$ tar xzf foo.tar.gz -C test-foo
$ tar xzf bar.tar.gz -C test-bar
$ diff -r --brief test-foo test-bar
...

But is there a straightforward utility for comparing the contents of
the files in two .tar or .tar.gz files without unpacking them?  (I'm
not interested in comparing the timestamps or permissions of the
archived files --- just the contents.)