Накратко:
CREATE PROCEDURE RESETGENERATORS
AS
DECLARE VARIABLE М BIGINT;
begin
select max(kod) from nomoperator into М;
М=case when М is null then 1 else М+1 end;
-- SET gen_nomoperator_id TO М;
M=gen_id(gen_nomoperator_id,gen_id(gen_nomoperator_id,-gen_id(gen_nomoperator_id,0))+M);

suspend;
end