That was simple after installation of postgresql i should change the postgres user password and my failure was because of that. The password can simply change through this commands under ubuntu 12.04 LTS:
sudo -u postgres psql
And then in psql:
\password
Now enter the new password and re-enter it.
That's OK! then you can simply sign in.
This way there is no need to change the configuration of pg_hba.conf
file.
In fact i failed to login because of my invalid password!