UTF-8 Problem ?

Hi Listers,
I want to insert some german specific characters (umlaut characters) into a table, but I am getting  the following 
Error message:
postgres=# EXECUTE  stmt (1, 1 , 1 , 'Grün')  ;
ERROR:  invalid UTF-8 byte sequence detected near byte 0xfc

Or 

postgres=# EXECUTE  stmt (1, 1 , 1 , 'MAßßtab') ;
ERROR:  invalid UTF-8 byte sequence detected near byte 0xdf

Here are my object/statement definitions :

A) PREPARE  stmt( int, int, int, varchar) as insert  INTO  part values ($1,$2,$3,$4);

B) 
postgres=# \d+ part                   Table "public.part"Column |          Type          | Modifiers | Description
--------+------------------------+-----------+-------------id1    | integer                | not null  |id2    | integer                | not null  |id3    | integer                | not null  |filler | character varying(200) |           |

C) 

postgres=# l\l      List of databases   Name    | Owner | Encoding
------------+-------+-----------db1        | user1 | SQL_ASCIIpostgres   | pg    | UTF8template0  | pg    | UTF8template1  | pg    | UTF8


How to solve my problem ? 

Best Regards. Milen