A consultant hired by the MTA to evaluate bids for the West Side rail yards is urging officials to reject both the Jets and Cablevision offers because they’re way too low, real-estate sources said.

Newmark & Company, brought in by the MTA to study the two bids and a third one from TransGas, believes up to $300 million has been “left on the table,” the sources said.

Newmark thinks the bidders lowballed the value of the site’s development rights – about 6 million square feet of prime real estate, they said. It pegs the rights as being worth close to $200 per square foot, meaning the site should fetch more than $1 billion, the sources said.

On Monday, the Jets bid $720 million and Cablevision – the owners of Madison Square Garden – offered $760 million for the site. TransGas bid $1 billion, but its offer has some many strings attached, it is not expected to fly.

The MTA originally thought the massive rail yards could get roughly $100 per square foot, then upped its estimate to $125.

The figures were lower than market value because there’s risk – the site needs to be rezoned as a light manufacturing area.

But a consensus has emerged that the city will rezone the site no matter what, meaning the rights should get close to market value, Newmark believes. “Why do it now? Why do it for $100?” asked a source familiar with the bids.

Newmark, a respected real-estate firm that has worked with the MTA for years, recently brokered the sale of a property not far from the Hudson Yards – a Verizon lot on West 42nd Street and 11th Avenue – for $200 per square foot.

Meanwhile, two MTA board members said the cash-strapped authority desperately needs to get top dollar for its site – and suggested it may not sell if the price wasn’t right.

“Just because it’s a bid doesn’t mean we will get a realistic price,” said board member Edward Vrooman. “If not, I wouldn’t sell it.”

Noting that the MTA faces a deficit of $1 billion in 2006, member Andrew Albert said: “You can’t fill these kinds of deficits with fare hikes and service cuts.”

Newmark’s views could sway the MTA board, which will meet Thursday to decide what to do with the bids.

The Jets bid, which has the endorsement of Mayor Bloomberg, includes $280 million for the stadium parcel and $440 million for the air rights above the arena, which would go to a group of powerful developers the team is working with. But it proposed to pay for the air rights only if the city rezones the area.

The MTA would have to take $350 million out of Cablevision’s $760 million no-strings-attached bid to pay for building the platform. Under the Jets’ plan, city and state taxpayers would pay for the platform, and the MTA could keep all of the bid money.

Rep. Anthony Weiner (D-N.Y.), a candidate for mayor, yesterday said the MTA board needs to take more time to decide the issue. “Ten days is not enough for something that could impact us for the next 90 years,” Weiner said.

Newmark officials could not be reached for comment.