SQL & PL/SQL

Hi,
I'm writing simple code db is 9.2.0.8

create or replace procedure gather_part_stats(p_schema in varchar2, p_table in varchar2)
as
l_quarter varchar2(8) := to_char(sysdate, '"Y"YYYY"_Q"q') ;
l_sql varchar2(2000) := 'exec dbms_stats.gather_table_stats(:schema, :table, method_opt => ''for all columns size 1'' , cascade => true , estimate_percent => 1 , granularity => ''PARTITION'', partname=>:part);';
begin
dbms_output.put_line('l_quarter: ' || l_quarter);
dbms_output.put_line(l_sql);
execute immediate l_sql using in p_schema, in p_table, in l_quarter ;
end;
/

Trying to gather table stats with selected partition but mess up something with ... something :)
I'm using using to avoid sql injection, please advice .

Error is:
SQL> exec gather_part_stats('TEST' , 'TEST');
l_quarter: Y2012_Q2
exec dbms_stats.gather_table_stats(:schema, :table, method_opt => 'for all columns size 1' , cascade => true , estimate_percent => 1 , granularity => 'PARTITION', partname=>:part);
BEGIN gather_part_stats('TEST' , 'TEST'); END;

*
ERROR at line 1:
ORA-00900: invalid SQL statement
ORA-06512: at "INSTALL.GATHER_PART_STATS", line 8
ORA-06512: at line 1

Regards
GregG