Scope Problem with Execute?

I have encountered what I think is a scoping problem with an EXECUTE
statement.

for test_record in select * from source_table
LOOP
for i in 0..9 loop
column_name := ''test_record.field_''||i;
insert_str := ''insert into output_table (output)
values (''||column_name||'')'';
execute insert_str;
end loop;
end loop;

I keep getting errors about not being able to find "test_record".

I can't find the right syntax so that the execute command can reference
the record (test_record). I've tried wrapping column_name in
quote_ident(), pulling out test_record into the insert_str literal,
splitting the record.field and quote_ident() both of them.

Any help would be greatly appreciated. Postgresql 7.2.3 on RedHat Linux
7.2 on Intel.

Thanks.
~Rob Storrs