Northern Rock was nationalised in February after getting into trouble.
Northern Rock is to more than double the number of people who work in its debt management department over the next year, the BBC has learned.
The move to redeploy staff suggests the bank is expecting to see a huge increase in the number customers who are struggling to pay their mortgages.
The details were in a document outlining how the firm proposes to trim about 2,000 jobs by 2011.
Northern Rock said the details could change after consultation with unions.
The bank's proposals would see the workforce of about 5,485 people reduced to 3,440 over the next three years, according to a document obtained by BBC Radio Newcastle.
Northern Rock is having to restructure and scale down following its nationalisation in February after the credit crisis forced it to seek emergency funds.
Many mortgage lenders are expecting to see a rise in the number of customers who are struggling to meet their mortgage payments as a result of a slowing economy and the prospect of higher unemployment and higher food and fuel prices.
There were the equivalent of 176 full-time workers in Northern Rock's debt management arm at the end of April, the memo said.
But it is proposed that this will increase to 444 by the end of March next year, before being trimmed to 282 by December 2011.
The bank - which is still trying to tempt savers with high interest rates - has no plans to make cuts among staff dealing with savings.
But it has already said that it wants to heavily downsize its mortgage book, from about £100bn to £50bn.
And with fewer customers expected, the number of customer service staff in its lending division will be cut from 1,152 to 478 by next year, falling to 369 by 2011.
The number of contact centre staff, who have been selling mortgages, will fall from 744 to 350 next year.
In other departments, staff carrying out training will be cut by two thirds, and the IT department will be slimmed down.
Northern Rock said that the document obtained by the BBC was intended for internal use.
"In the interests of openness and transparency, Northern Rock believes it is right to update staff on a regular basis throughout the consultation process with Unite and other employee representatives," it said.
"The indicative figures noted in this staff communication are subject to the consultation process and exploration of any other viable alternatives."
The Newcastle-based bank had primarily relied on borrowing from money markets, rather than its own deposits, to fund mortgage lending. As the credit squeeze took hold it struggled to finance its business model.
The move to seek emergency funding from the Bank of England triggered the first run on a UK bank in more than a century.
Earlier this month, the executive chairman of Northern Rock, Ron Sandler told MPs that, as things currently stand, Northern Rock would be able to repay the £26.9bn Bank of England loan by the end of 2010.
The bank expects to repay about £7bn of the loan by the end of 2008, he said.