Hedge fund activist Leon Cooperman is wavering in his earlier support for the nation’s biggest newspaper merger as falling stock prices put the deal in jeopardy, The Post has learned.

Cooperman, whose Omega Advisors owns a 9.9% stake in New Media Investment Group, is telling people he will vote down New Media’s planned merger with USA Today owner Gannett Co. unless the stock reverses its recent slide, sources said.

New Media, whose Gatehouse Media owns 152 regional newspapers across the country, announced on Aug. 5 that it would buy Gannett in a cash-and-stock deal valued at $1.4 billion.

The deal’s value has plummeted to $1.2 billion, however, as investors flee New Media, which will be used to buy Gannett.

Cooperman, who began buying New Media stock in February when it was trading at more than $13 a share, thinks the deal will only work if New Media’s shares rise above $8 a share, sources said.

The stock, which has dropped 25% since the deal was unveiled last week, closed down 2.4% Monday, to $7.89 a share.

Hedge fund Alden Capital, headed by Heath Freeman, came out against the deal on Friday, when it announced a 9.4% stake.

Together, Cooperman and Alden own nearly 20% of New Media’s shares.

Shareholders of both companies need to OK the merger for it to go through. They still have time to turn things around, however, as the vote is expected to be held in November.

Cooperman’s waffling support comes as New Media Chairman and CEO Michael Reed plans to hit the road Tuesday with Gannett CEO Paul Bascobert to sell the deal to investors.

As The Post reported last week, the execs aim to use the roadshow to convince investors that the merger is the best way forward, including $300 million in savings.

Stock issues aside, the Bronx-born Cooperman, 76, has been a proponent of a New Media/Gannett merger. In fact, his Omega slightly added to its stake on Aug. 5 and Aug. 7 in anticipation of New Media becoming the nation’s largest newspaper publisher, sources said.

Alden, which owns the Denver Post and Boston Herald through newspaper chain MNG Enterprises, is opposing the deal because it wants New Media to merge with it instead, a source with direct knowledge of Alden’s thinking said.

Meanwhile, some Tribune Publishing shareholders are urging the board to consider making a $10-a-share counterbid for Gannett. But that strategy would require Tribune to convince Gannett shareholders that they would be better off taking a lower all-cash offer from Tribune than the cash-and-stock deal that New Media is proposing, which contains only $6.25 per share in cash.

Gannett shares rose 6 cents Monday, to close at $9.81.

New Media can break its deal with Gannett for a relatively low price, giving it the ability to pursue other options, sources said.

New Media didn’t return a call for comment.