Three operating theatres could be shut in a bid to save a cash-strapped hospital millions of pounds.
A ward with up to 35 beds at Crawley Hospital could also be closed and patients forced to travel miles to other hospitals for surgery.
The temporary changes, which could save up to £1.7 million, were today condemned by patient groups and campaigners fighting to save vital services at the hospital.
They are already angry at the loss of accident and emergency, maternity and children's inpatient services from Crawley to Redhill, Surrey.
Michael Edwards, from Crawley, who was part of the unsuccessful campaign to have a new hospital built at Pease Pottage, near Crawley, said: "This is appalling. We have been promised that there are so many good developments for Crawley but once again more services are being lost. At this rate we are not going to have anything left and Crawley will end up being closed down."
Surrey and Sussex Healthcare NHS Trust is facing a financial crisis. It is already £17 million in the red and could have a £38 million deficit by March unless it takes urgent action.
It wants to stop most routine operations at Crawley Hospital as part of plans to save £17 million this year.
Patients waiting for an operation will either go to East Surrey Hospital in Redhill or be offered alternative places to have their operation and treatment.
This will include the privately-run diagnostic and treatment centre at East Surrey Hospital which has a five-year contract with the trust to provide services.
Muriel Hirsch, secretary of the Crawley Pensioners Action Group which is campaigning to bring hospital services back to the town, said: "It seems we are paying the price for years of Government under-funding and could be losing yet another service.
"The board may say it is only temporary but seeing the financial problems it has I'm worried it will probably be a permanent move.
"If so, it will probably mean patients having to go further afield for their surgery. This makes no sense. Surely it is better for people to get their treatment closer to home.
"Even if people do go to East Surrey, access is still difficult, especially for people living further afield, like Horsham. Traffic can be bad and getting the bus or train is not easy for many either.
"We should have a new hospital. The town is growing all the time but the hospital services are getting less. It does not look good."
Finance director Duncan Brodie is due to tell the trust board tomorrow savings plans already agreed do not seem to be working.
The financial crisis is mainly caused by spending extra money on expensive agency staff to cover shifts.
The trust wants to reduce the amount of work it does so it only has to use permanent staff.
The changes could save the trust between £1.4 and £1.7 million.
Under the plans patients who have been waiting seven months for a routine operation will be given a choice of a different place to have their surgery.
The first batch of more than 200 waiting for surgery will be contacted in the next few weeks.
Trust medical director Tony Gordon-Wright, said: "As an acute hospital trust our first commitment continues to be to those patients who are seriously ill."
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