If your interviewer asked for company vacation letter, you can tell him/her that you want to get the visa first before submitting your leave application and buy air tickets.
you are grovernment employee, you should no problem to get the vacation paper..?
you also better bring in last 3 months bank statements. and paid studs.
plus you need a good reason why you want to visit US.....
the chance look good for you... so, good luck la.