* Escalating spat over severance payments to senior execs
* Raises questions about management at BBC, will alarm NYT
* Ex-BBC head, current NY Times boss angry over "untruths"
* BBC Trust says accusation "bizarre"
LONDON, Sept 6 (Reuters) - The BBC's former director general Mark Thompson has accused the head of its governing body of misleading Britain's parliament about huge pay-offs to senior executives, in an escalating spat that has put the two men's reputations on the line.
Thompson, who quit the British broadcaster last year to become chief executive of the New York Times, is under fire over payments of 25 million pounds ($40 million) made to 150 departing BBC staff from 2009 to 2012.
The scale of the severance payments, many of them made as austerity cuts swept Britain, angered politicians and members of the public, who fund the broadcaster through a compulsory licence fee.
The head of the BBC Trust, Chris Patten, told a parliamentary hearing in July he was shocked by the size of some of the pay-offs and unaware some were more than required under contractual terms.
But in a scathing written submission to a parliamentary committee, released on Friday, Thompson accused Patten of knowing about the payments and including "unspecific untruths" and "inaccuracies" in his evidence.
Thompson, who is due to appear in front of the committee on Monday, said he had emails to prove this.
Patten, a senior British conservative politician best known for handing control of Hong Kong back to China in 1997, rebutted the attack by telling reporters he "had no concerns at all" about Thompson's submission that the Trust called "bizarre".
The stand-off between the two men has raised questions about the ethics and management of the BBC under Thompson and Patten and will cause alarm across the Atlantic at the New York Times.
"It has become daggers drawn and it is hard to see how their positions are reconcilable," said media analyst and former ITV executive Steve Hewlett.
"Ethics are central to the New York Times and if it transpires that Thompson has misled people, he could be in trouble. Similarly if the Trust was told more then they are letting on then Patten will be a very difficult position."
The inquiry into payouts to senior BBC staff was triggered after Thompson's successor, George Entwistle, left the BBC late last year after just 54 days in the top job with a payoff of 450,000 pounds.
He stepped down to take responsibility for a BBC news report which falsely accused a former senior politician of child abuse and allegations the corporation covered up decades of sex abuse by one of its late stars, Jimmy Savile.
A National Audit Office report found a string of huge payments were made to departing executives who were not always entitled to the money.
It is the details over severance payments to former deputy director general Mark Byford and to former marketing chief Sharon Baylay that have come under particular scrutiny and caused the major disagreements between Thompson and Patten.
Byford departed with a total payout of 949,000 pounds and Baylay's settlement was worth 395,000 pounds.
The BBC Trust said it rejected Thompson's suggestion that Lord Patten and BBC Trustee Anthony Fry misled parliament's Public Accounts Committee (PAC).
"We completely disagree with Mark Thompson's analysis, much of which is unsubstantiated," the Trust said in a statement.
The BBC's director of human resources Lucy Adams, who has been fiercely criticised over the size of the payoffs, announced last week that she would leave the corporation next year.