The document, which looks at local services and how they should develop in line with changes in the health service, suggestes Preston could be combined with either Chorley or South Ribble, or trusts in Blackpool or Accrington.
It is currently being considered by local politicians.
Liberal Democrat leader, coun Bill Chadwick, has slammed the idea and is concerned a merger would mean specialist cancer services being centralised at Christie Hospital in Manchester.
Coun Chadwick said: "Money is desperately short in the NHS and staff are working long and hard, yet cannot keep up with the pressure.
"One benefit of the two existing trusts in Preston and Chorley having separate budgets is that money cannot be taken away from clinics and other community facilities to prop up acute services.
"It worries me that other proposals could see Blackpool linked to Preston and that two specialist services covering cancer care and neurosurgery have a heavy bias towards Manchester."
But Hugh Lamont, spokesman for the NHS executive North West, said the changes were merely suggestions, designed to encourage debate.
He said: "There are no plans to merge these trusts.
"The document is a discussion piece aimed at stimulating debate as to the best way the NHS should organise itself to improve local healthcare."
"All we are saying is look at the situation on a local level and see if it is the best way to deliver services.
"We want health authorities, trusts, community councils and GPs to engage in conversation and come back to us with plans - one thing that might come out is that arrangements should stay the same.
"We're just asking for the debate to happen and we welcome the input of politicians in the debate."
Converted for the new archive on 14 July 2000. Some images and formatting may have been lost in the conversion.
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