With too many unknowns regarding the 2010 and 2012 Olympics — including where they’ll be held — CBS announced Monday that it wouldn’t make a bid for the Games.

That leaves ABC, NBC and Fox in the running to carry the Winter 2010 and Summer 2012 Games, a package that’s expected to fetch at least $2 billion. Execs from the three nets will fly to Switzerland this week to pitch the Intl. Olympic Committee officials on why their respective nets should land rights to carry the Games.

CBS and ABC/ESPN were slated to pitch the IOC on Thursday, while Fox and NBC are scheduled to make their presentations on Friday. It’s unclear whether that schedule will change now that the Eye is out of the running.

CBS Sports prexy Sean McManus opted to tear up his ticket to Europe after Eye execs decided it was already covered sports-wise with big-bucks packages like the NFL and the NCAA basketball tournament.

“CBS is the best positioned network in terms of overall programming and sports lineup,” the web’s toppers said in a statement. “With all of the uncertainties surrounding two events that don’t conclude for another nine years, committing significant rights and production expenses to the 2010 and 2012 Olympic Games is not the best use for our resources.”

Beyond the question of where the Olympics will be held — which could make a huge difference in terms of viewership, depending on whether events are broadcast live or taped –CBS execs were concerned over the impact of unforeseen international events, such as terrorism.

Speaking to stations at last week’s CBS affiliates meeting, McManus hinted that nabbing the Olympics was not necessarily a major objective for the net.

“We’ll do what’s in the best interest for CBS and its affiliates before we commit to any bids,” McManus said.

NBC holds the rights to carry the Olympics through 2008, having paid nearly $4 billion for a five-Games package.