declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE PTOVTA_CAT_IND ADD INDTOTALBUS NUMBER (1,0) DEFAULT 1';
    exception when column_exists then null;
end;

/

declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE PTOVTA_CAT_IND ADD INDEMBARCADA NUMBER (1,0) DEFAULT 1';
    exception when column_exists then null;
end;