What is the simplest way to define a local variable in Oracle?

In the SQL Server, I can define local variables like this.

declare @id number := 1000

select * from tbl_A where id = @id;
select * from tbl_B where id = @id;

It is very convenient. I tried to do same thing in PL/SQL but it doesn't work.

DECLARE id number;
select 1000 into id from dual;

Do you know how to do something similar? The simplest method is my objective.