* Escalating spat over severance payments to senior execs
* Ex-BBC head, current NY Times boss cites "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 large payments 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 facing scrutiny over payments of 25 million pounds ($40 million) made to 150 departing BBC staff from 2009 to 2012.
The scale of some 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 committee hearing in July he was shocked by the size of some of the payments and unaware a number were more than required under contractual terms.
But in a written submission to the Public Accounts Committee (PAC), released on Friday, Thompson said: "The picture painted for the PAC by the BBC Trust witnesses ... was - in addition to specific untruths and inaccuracies - fundamentally misleading about the extent of Trust knowledge and involvement."
Thompson said in a statement emailed to Reuters by a New York Times spokeswoman on Friday that he had backed up his submission with evidence and would not comment further until he appeared on Monday before the committee, a body which oversees government expenditure.
Patten, a senior British conservative politician best known for handing control of Hong Kong back to China in 1997, told reporters he "had no concerns at all" about Thompson's submission. He will also appear at the hearing on Monday.
The BBC Trust said it rejected Thompson's statement, and called it "bizarre".
The stand-off between the two men has raised questions about which senior managers were aware of the payments and whether public money was used appropriately. A spokeswoman from the New York Times told Reuters: "We're looking forward to Mark's full testimony on Monday."
"It has become daggers drawn and it is hard to see how their positions are reconcilable," said Steve Hewlett, a media analyst and former executive with British broadcaster ITV.
"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 payments to senior BBC staff was triggered after Thompson's successor, George Entwistle, left the BBC in November last year after just 54 days in the top job with 450,000 pounds, which the National Audit Office later said was equivalent to a 12-month notice period set out in his contract.
Entwistle 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 in July, requested by the Public Accounts Committee after a public outcry over the size of payments to Entwistle and other executives, found a number of large sums were paid to managers, some of them exceeding contractual requirements.
Mark Thompson, in his recent submission to the committee, said the Trust had been aware, in particular, of severance payments to former deputy director general Mark Byford and to former marketing chief Sharon Baylay.
Byford departed with 949,000 pounds and Baylay's settlement was worth 395,000 pounds - both of them 12 months' pay in lieu of notice on top of redundancy payments - the National Audit Office report said. It did not say that those payments had exceeded contractual requirements.
The BBC Trust said it rejected Thompson's suggestion that Lord Patten and BBC Trustee Anthony Fry misled the parliamentary committee.
"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 payments, announced last week she would leave the BBC next year, saying it was time for a new start after five years at the corporation.
In a submission to the PAC released on Friday she said she had made a mistake in her earlier evidence to the committee and now did recall drafting a memo sent by Thompson to the Trust relating to the severance payments to Byford and Baylay.
Adams is also due to appear at the hearing on Monday.