* Marston's rejects 666 mln pound proposal

* Says proposal 'very significantly undervalues' it

* Shares rise 6%

Feb 1 (Reuters) - Marston's rejected a 666 million pound ($910 million) takeover proposal from Platinum Equity Advisors on Monday, saying it significantly undervalued the British pub operator.

Shares in the London-listed firm, which fell 40.6% in 2020, closed 6.1% higher at 86.2 pence, still well below Platinum Equity's offer of 105 pence per share.

Marston's, the brewer of Pedigree, Hobgoblin and Lancaster Bomber beer, said this was the U.S. private equity firm's third takeover proposal, following offers of 88 pence and 95 pence a share in December which it unanimously rejected.

Los-Angeles based Platinum Equity, which was founded in 1995 by American businessman Tom Gores, who owns the Detroit Pistons basketball team, did not respond to a request for comment.

Under stock market rules, Platinum now has until close of play Feb. 26, to make a formal offer.

The British pub sector has been in decline for years and has been hit hard by forced closures during coronavirus lockdowns, as have restaurants and other leisure businesses.

Last year, Marston's said it planned to cut about 2,150 jobs and called for more government support after it posted an annual loss of 22 million pounds.

On Monday, the company highlighted its joint venture with the UK division of Danish brewer Carlsberg, saying that the deal realised significant value on completion last year and is anticipated to continue to do so.

It also played up its recent agreement to operate 156 SA Brain pubs in Wales, which it said is expected to boost its earnings.

Platinum Equity's latest offer of 105 pence represents a premium of about 40% to Marston's closing price on Thursday, a day before the British company publicly confirmed the approach.

But Marston's, which runs about 1,400 pubs, said the offer was still 19% below its pre-coronavirus share price.

Two other British pub operators have been taken private in recent years. Greene King agreed to a 4.6 billion pound takeover by Hong Kong's CK Asset in 2019 and Ei Group was bought by Slug and Lettuce owner Stonegate owner last year. ($1 = 0.7317 pounds) (Reporting by Tanishaa Nadkar in Bengaluru; Editing by Aditya Soni and David Clarke)