Dumbledore's spies

[Sophie]

No: HPFGUIDX 81541

I just came across an interesting passage in PoA ch 10 (Marauder's map).
It's when Fudge, McGonagall, Hagrid, etc. were talking at three
broomsticks.
Getting ready to tell the story about the potters' secret keeper, he says:
"Not many people knew You-know-who was after them.  Dumbledore... had
a number of useful spies.  One of them tipped him off, and he alerted
James and Lily at once."

How likely is it, do you think, that Snape was that spy?  What sort of
wierd dynamic would that set up?  Snape would have made an effort to
save the life of James ad Lily.  That must count for something. 

Sophie