I've been working in France since Sept 2009, and expect to continue until Sept 2010. After Sept 2010, I will have been out of the USA for at least 330 days, and therefore qualify for the earned income exclusion. Can I take the foreign income exclusion for my French earnings on my 2009 return, or do I have to wait until I file the 2010 return?
If I have to wait, what happens to the 2009 earnings? Did I lose the opportunity to exclude that income?

Of course, I am having French income tax withheld from my pay. If I can't exclude the 2009 earnings on my 2009 return, can I instead claim the credit for foreign taxes paid on my 2009 USA return?

You need to wait until you have met the 330 day requirement before you can claim the exclusion. If you need to extend beyond the normal extension period, see Form 2350.