Okay, m'eclairer, I'll start off by saying I did exactly the same AS's you want to do, and dropped History at A Level because I figured that most offers tend to be for three grades, so why give myself the extra work (not very Oxford I know, but I was AWFULLY fond of my 24 frees a week
I applied to Merton (dicey, yes) and was pooled and got into Oriel with an offer of three A's despite not having done maths and the extent of my maths skills being basic differentiation. I really really really hated logic, but in all honesty, there appear to be just as many people who have done maths who also didn't like it. It is rather more mathy than any of your AS's, but if you're predicted an A* at GCSE, I can't foresee there being any major problem. If you're going to hate doing AS Maths, don't do it, simple as.
On the subject of Government and Politics, my three A Levels were Economics, Eng Lit, and Politics, and I got offers from Oxford, Durham, Bath, Exeter, and York, so I wouldn't say that any of them put at a particular disadvantage. None of them, even Politics, are THAT wishy washy, and as it's related to what you want to do, and especially if you get predicted an A, it can only be a good thing (IMO at least).
Hope that helped, but most of all I'd say DON'T WORRY. It's not a foregone conclusion that you'll get in (or not) no matter which A Levels you do, and if you enjoy what you're doing, you'll find it a LOT easier to come over well at interview, which is the real clincher. So good luck!