* GE will have right to redeem new NBCU stake for cash

* Deal unlikely to be announced before 3 to 4 weeks

* News Corp, Liberty Media interested in NBC - CNBC (Adds deal details, byline)

NEW YORK, Oct 12 (Reuters) - General Electric GE.N could start to exit a new NBC Universal joint venture with Comcast Corp CMCSA.O as soon as three-and-a-half years after the ink is dried, two people familiar with the talks said on Monday.

Comcast is in talks with NBC Universal’s parent company GE to buy a controlling stake in the joint venture that has broadcast and cable channels as well as movies and theme parks

Under the proposal, NBC Universal would become a joint venture 51 percent owned by Comcast and 49 percent by GE. It would be valued at around $30 billion. Comcast would contribute around $4 billion to $6 billion in cash as well as its collection of cable networks to pay for its stake.

The deal has involved a lot of back and forth negotiations between both sides.

But GE, which has been pressured by investors to offload its 80 percent stake in NBC Universal, is considering a host of proposals for the unit, as partner Vivendi SA VIV.PA explores whether to sell its 20 percent stake.

GE has negotiated a redemption option, that will give it the right to redeem all or part of its stake in the so-called ‘newco’ in exchange for cash at the three-and-a-half year mark and at a seven-year mark, the sources said. They spoke anonymously because the talks are private.

The new NBC Universal is expected to be able generate enough cash to pay down $9 billion in debt that would be added to its books as part of the deal, and purchase the rest of the company from GE.

“There’s a sense there will be sufficient cash flow to do that,” said one person familiar with the talks.

But under the deal being negotiated, Comcast would also provide a backstop of around “mid-single billion” dollars, if there is insufficient cash to buy out GE’s stake within the agreed time frame, according to the sources.

Talks between Comcast and GE continue, and it is unlikely the two sides will reach a deal in the next three-to-four weeks, a second source said.

Rupert Murdoch's News Corp NWSA.O and John Malone's Liberty Media Corp LINTA.O are also interested in NBC Universal, though neither has approached GE so far, CNBC reported, citing sources.

News Corp, which owns the Fox cable network and local TV stations, had been seen as a less likely bidder, analysts have said, because taking a stake in NBC might raise antitrust concerns with the U.S. government.

Liberty Media has been seen as possible bidder for a minority stake in NBC Universal because of its history of taking minority stakes in big media companies.

GE is likely to prefer a sale to Comcast despite the complex structure of the deal being discussed, rather than explore options that would bring even more complexities, the source added.

Spokespeople for GE, News Corp and Liberty Media declined to comment. (Reporting by Yinka Adegoke; additional reporting by Robert MacMillan in New York and Scott Malone in Boston, editing by Leslie Gevirtz)