Loki vs Doctor Who & Martha

Can the Doctor stop Loki from unleashing his Chitaur...Chitari...those alien things

No.

Yes.

It depends how much time they have beforehand. The Doctor has defeated beings more powerful than Loki, stopped invasions on various worlds, and essentially does whatever the heck he wants to.

Can the Doctor prevent Loki from opening the portal? No, I don't think so. However, the Doctor would be able to shut down the portal and save Earth. That's just what he does. I don't think Martha will be much help though.

The Doctor has stopped far worst than Loki and an army of "those alien things".

@The_Young_Wolf said:

The Doctor has stopped far worst than Loki and an army of "those alien things".

the question is if he could stop him from summoning those things

He's the Doctor, of course he wins. Martha isn't as helpful as Donna would be, but the Doctor still wins. Probably blows up the machine, or just disables it, with his sonic probe.

The Doctor can easily do this, and Martha is only there to stop him from Annihilating the entire Asgardian race.