erro com SP

amigos, qual o problema com esse comando:

CREATE PROCEDURE SP_DIU_CUSTOMER( OPERACAO INTEGER, CUST_NO INTEGER, CUSTOMER VARCHAR(40), CONTACT VARCHAR(25), PHONE VARCHAR(15), CITY VARCHAR(15) )
AS begin
if (operacao=1) then delete from customer where cust_no=:cust_no;
if (operacao=2) then insert into customer(cust_no,customer,contact_first,phone_no,city) values (:cust_no,:customer,:contact,:phone,:city);
if (operacao=3) then update customer set cust_no=:cust_no, customer=:customer, contact_first=:contact, phone_no=:phone, city=:city where cust_no=:cust_no;
end

interbase...


abraços