How To Use Variable To Receive The Result Of A Select Statment. ?

Good morning;

My Problem is :im my transaction i use insert code like the following :

" Insert into TAB1 (F1,F2,F3)
select a.F1,b.F2,b.F3 from TAB2 a,TAB3 b
where a.KY1= b.KY1 and b.ORDN in
(Select ORDN from OTAB where USER_ID = 'MIKE')"

In order to optimise my code ,
instead of using a subquery in my select
(I have different insert in my transaction with the same subquery).
I would like to DECLARE a varibale which will contain the select of the Subquery.
and then use it im my different insert. some thing like this.

" BEGIN TRANSACTION
DECLARE @OrdSelect int
Set @OrdSelect = (Select ORDN from OTAB where USER_ID = 'MIKE')
Insert into TAB1 (F1,F2,F3)
select a.F1,b.F2,b.F3 from TAB2 a,TAB3 b
where a.KY1= b.KY1 and b.ORDN in @OrdSelect
COMMIT Tran "

I know that the @OrdSelect will receive the last value of the select not an array of values. which will make my transaction incorrect.
I dont want to use Cursor to resolve this issue Too.

Thinks.