FRANKFURT (Reuters) - U.S. cable company Liberty Global is preparing a takeover offer for Kabel Deutschland, Manager Magazin reported, sending shares in Germany's biggest cable company higher.

By preparing a bid, Liberty Global wants to steal a march on UK-based telecommunications company Vodafone, which is also interested in buying Kabel Deutschland, the monthly magazine said in an excerpt of an article to be published on Friday. The excerpt did not cite sources.

Kabel Deutschland and Liberty Global declined to comment.

Any attempt by Liberty Global to buy Kabel Deutschland, which has a market value of 6.2 billion euros ($8.1 billion), would likely meet resistance from anti-trust regulators as the U.S. company already owns Unitymedia Kabel BW, Germany's No. 2 cable company.

The German cartel office blocked a similar deal earlier this year. Kabel Deutschland had wanted to buy Germany's No. 3 cable company Tele Columbus, but the regular said such the move would cement a duopoly and crimp competition.

A banker familiar with the sector said he could imagine that Liberty Global was only preparing a bid to drive up the price of Kabel Deutschland beyond what Vodafone would be willing to pay.

A source had told Reuters earlier this year that Vodafone was considering a bid for Kabel Deutschland to expand its services in Europe's biggest economy.

Shares in Kabel Deutschland were trading 5.2 percent higher at 73.94 euros by 0955 GMT.

On Monday, Liberty Global won unconditional EU regulatory approval for its $15.8 billion takeover of Britain's Virgin Media.

(Reporting by Maria Sheahan; Additional reporting by Sabine Wollrab and Arno Schuetze; Editing by Mark Potter)

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Liberty Global preparing Kabel Deutschland bid: report