error : syntax error at or near $1 for over select rows

This is the error i am getting when calling select * from
cas_reset_qi_changedate('CAS','2003-02-03'

ERROR:  syntax error at or near "$1" at character 25
CONTEXT:  PL/pgSQL function "cas_reset_qi_changedate" line 15 at for over
select rows

pgsql function :
CREATE or replace FUNCTION qe13.CAS_RESET_QI_CHANGEDATE (VARCHAR,TIMESTAMP)
RETURNS INTEGER AS '


DECLARE
        AGR_UNID ALIAS for $1;
        M_COMM_CLOSE_DATE ALIAS for $2;
        DEFAULT_LOWEST_DATE     timestamp default ''1900-01-01 00:00:00.0'';
        vQuotaInstanceGID       varchar(34)     default null;
        vQIStartDate            timestamp;
        vQIEndDate              timestamp;
        for1                    record;

BEGIN


        FOR for1 in select qi.tril_gid as vQuotaInstanceGID,qi.startdate as
vQIStartDate,qi.enddate as vQIEndDate from cm_quotainstance as qi, cm_quota
as q, fs_agr as a where a.fs_unid = AGR_UNID and a.fs_model = q.model and
qi.quota = q.tril_gid LOOP

                        if (vQIStartDate > M_COMM_CLOSE_DATE OR vQIEndDate
<= M_COMM_CLOSE_DATE) then
                update  cm_quotainstance set changedate =
DEFAULT_LOWEST_DATE where tril_gid = vQuotaInstanceGID;
                end if;
        END LOOP;

        RETURN 0;


END;
' LANGUAGE 'plpgsql';

I know the problem is that we cant use a variable name in a select query.
But then how can I use this variable later in "if" statement (say
vQIStartDate variable)
Thanks and Regards,
Vinita Bansal

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