psql without password

Hello,
I have the following command in a script:
ROOMID=`echo "$USER_PW" | psql -c "select nextval('contract_roomid_seq');"
"$DB_NAME" "$DB_USER" | awk -F" " '{if ($1 > 0 && $1 < 3000000000) print
$1}'`
Now I have the next valid roomid in the variable ROOMID.

With the psql-version 7.1.0 it works fine. But with psql-version 7.2.1 I
have to type the password again.
I have several of this commands. So I have to type the password several
times.
What can I do to give the password in one command-line?

Best regards
Heinrich

Heinrich Retzlaw - Software Developer
ETM Deutschland GmbH
Adenauerstraße 20-A1, D-52146 Aachen
Tel. +49/2405/483-0, Fax -707
E-Mail: hretzlaw(at)etm(dot)at
Web: http://www.etm.at http://www.praedico.com