./dir/index.htm or only ./dir/

What's better

[fandangood]

1) www.xyz.com/directory/ (PR4)
2) www.xyz.com/directory/index.htm (PR4)

On my site internal link are all direct to www.xyz.com/directory/index.htm but in the Google serp in the last 2 month alternate the result number 1 or number 2. Can Google penalize me?

I think that the best is Permanent Redirect by .htaccess from www.xyz.com/directory/ to www.xyz.com/directory/index.htm. Is it correct?

Thanks in advance