UPDATE 2-Telenet eyeing joint bid for KPN's BASE -sources

* Telenet seeking private equity bid partners -sources

* KPN weighs Belgium exit as America Movil tender offer looms (Adds further context and background)

By Sophie Sassard and Victoria Howley

May 22 (Reuters) - Belgium's largest cable operator Telenet is talking to private equity firms about making a joint bid for KPN-owned BASE, the country's third-biggest mobile phone company, people familiar with the process told Reuters.

Blackstone, Cinven, Providence, Bain and KKR are among possible partners, the people said.

Dutch telecom group KPN is weighing a sale of the Belgian business at the same time as it seeks ways to counter America Movil's tender offer for 28 percent of its shares, which it sees as undervalued.

It is not clear whether KPN's broader defence will slow the BASE sales process, in which presentations to potential bidders were initially slated to go out in the next two or three weeks.

"Every private equity player would try to team up with Telenet as there is no trade rival that could offer the same synergies here," said a person at one of the interested private equity firms.

KPN could raise between 1.6 billion and 1.8 billion euros ($2.3 billion) from the sale of BASE, based on 280 million euros of estimated EBITDA for 2012, and multiples of between 5.5 and 6.5 times.

KPN declined to comment.

Telenet, controlled by Liberty Global via a 50.2 percent stake, is reviewing a bid for BASE that would limit its owner's financial contribution by teaming up with a private equity firm, the people said.

It is consulting advisory firms Lazard and Goldman Sachs on the matter, the people said. The two banks declined to comment.

Telenet markets TV, phone and broadband services to households and companies in Belgium.

It holds a mobile licence but has not built a network, and buys minutes from Belgian rival Mobistar so as to offer clients mobile services.

If it were to acquire BASE, it could offer its 4.4 million subscribers an all-in-one bundle including mobile calling over its own network.

Acquiring BASE would be a first major step into mobile for international cable company Liberty Global, which has traditionally focused on its core business.

Liberty has become a major player in European cable, with a presence in 11 countries, by buying up smaller cable operators.

It now owns the Netherlands' biggest cable operator, UPC, and the second biggest in Germany, KBW.

Until now, Liberty has been reticent to take on the extra expense and complication of running a mobile business, although it did look at bidding for Orange Switzerland when it was sold by France Telecom last year.

A move for BASE could indicate that Liberty is willing to look at mobile opportunities when they can be done with low risk and without big spending upfront.

"Liberty sees the potential for bringing together cable and mobile businesses in the next five years, but the two businesses are very different so they also have misgivings," said a person close to the BASE situation.

"They want to get their toes wet without making a bold move."

Liberty could not be immediately reached for comment.

The next question Liberty will face in its mobile strategy will be whether to bid for a fourth generation mobile licence in the Netherlands, which will be sold later this year.

The Dutch regulator has set aside blocks of relatively cheap spectrum for new entrants in a bid to increase competition in the three-player mobile market.

Such a development would be bad news for KPN on its home turf, where it earns most of its revenue and profit.

With profit falling at home, KPN's debt ratios are creeping closer to its self-imposed ceiling of 2.5 times EBITDA earnings, making it tougher for it to keep dividend pledges.

Like its peers, KPN saw its performance dented by competition-boosting regulatory measures and the rise of smartphones from Google and Apple, whose messaging apps allow users to avoid charges for voice and text.

Selling its Belgian arm would buy KPN a little time and allow it to pay down debt. An exit from Germany, a growing business that requires steep investments to keep up with larger rivals, would be a bolder move.

The recent tender offer from America Movil, which would make the Mexican telecom giant KPN's largest shareholder, could halt or slow the exit from Belgium and Germany.

($1 = 0.7838 euros) (Reporting by Sophie Sassard and Victoria Howley in London, and Leila Abboud in Paris; Editing by David Hulmes)