Unable to user pg_restore

Dear Friends,

I have created a compressed backup for the database - sampledb using the following
$ pg_dump -h 192.128.2.51 -v -u -f /home/db_repository/sampledb20031020.sql.tar.gz wats -F c

while I try to restore this with the pg_restore function as follows
$ pg_restore -d sampledbtest -f /home/db_repositorysampledb.sql.tar.gz -F c -v -c -O -h 192.128.2.51 -p 5432 -u
User name: postgres

It never prompt for password, so I just typed the password , and get the error as follows,
postgres
pg_restore: [archiver] did not find magic string in file header
$

Anyone could advise me on this pls.

Kumar