The decision has dismayed objectors to the Wandylaw scheme, near Ellingham, who had been banking on the council's support at the inquiry starting in Berwick on September 16.
Nick Blezard, chairman of Save Northumberland's Environment (SANE), said: "We are very disappointed at the council's decision.
"It must weaken our case that the lead objector will no longer be appearing at the inquiry but our objections still stand and will appear at the public inquiry."
Councillors reluctantly took their decision after receiving legal advice that three of their original reasons for refusing RidgeWind's application - its detrimental impact on the landscape, tourism and local economy - were now weak.
They are now pinning all their hopes on the Ministry of Defence (MoD) which is still expected to outline its concerns at the impact of the turbines on the air defence radar at nearby RAF Brizlee Wood.
However, as the council cannot provide any specific evidence on this it has decided to withdraw from the inquiry and rely on the MoD to make its own case.
Coun James Hutchinson said: "We are having to nail our colours to the MoD's stance because our other arguments have been put to bed."
Coun Dougie Watkin added: "It's frustrating and very disappointing but it seems we have little choice."
The decision comes in the aftermath of the recent approval by the government for an 18 turbine wind farm at neighbouring Middlemoor.
Middlemoor had faced similar objections to Wandylaw, yet a government planning inspector felt it could be approved as long as a solution was found to mitigate the turbines' effect on the Brizlee radar.
The inspector deemed landscape objections were outweighed by the scheme's renewable energy benefits, while tourism was not found to be a valid objection.
Council barrister Colin Crawford explained there had been a marked shift in government policy in favour of renewables since the council's original decision.
In addition, whereas the draft version of the regional spatial strategy planning document had assessed a wind farm's impact on the wider setting, the final version only takes into account proposals close to their boundaries.
"Detrimental impact on tourism has never been upheld by an inspector as a reason for refusing a wind farm," Mr Crawford added.
Councillors were told that if the authority did not present evidence to justify refusal it would be more likely to be forced to pay the appellant's costs.
Coun Richard Patterson, acting planning committee chairman, said: "This was a very difficult decision for members to make.
"When we made our original decision to refuse the Wandylaw application last October, we thought that we had a very strong case.
"However, this has now changed, particularly now that we have the finalised regional spatial strategy and also the Secretary of State's decision on the Middlemoor inquiry," he added.
"We have therefore had to concede that there is now no point in the council being represented as a formal objector at the forthcoming public inquiry."
However, SANE disagrees and will be putting forward exactly the same objections at the public inquiry.
Mr Blezard said: "What the council do is up to them but we think there is still a strong argument when it comes to the wind farm's impact on the landscape and tourism.
"There are far more planning policy guidelines than the regional spatial strategy which the council seems to be basing its decision on.
"Just as was the case at Middlemoor, we think the same arguments apply at Wandylaw."
Objectors are particularly concerned at the cumulative impact if Wandylaw is approved. Alongside Middlemoor, it would create a 28 turbine landscape within two miles of each other.