The 250-year-old barracks outside Inverness is among a number of bases at risk of closure as part of a Ministry of Defence review.
Highland Council leader Margaret Davidson and MP Drew Hendry met Defence Minister Mark Lancaster in London.
Mr Hendry said: "It is disappointing that we still have no firm answer."
He added: "Following our discussions, the minister can be left in no doubt about the military, social and economic value of Fort George - both to our local economy and to our armed forces.
"We have urged him, yet again, to put an end to this uncertainty and to seriously consider the potentially-damaging impact of this decision on the Highlands."
The Ministry of Defence review is due to report by the end of October.
Following the Westminster meeting, a spokesman for the MoD said: "Every penny made from the sale of sites will be invested back into defence on things like the new maritime aircraft at Lossiemouth or the new ships being built on the Clyde.
"While no final decision about future sites has been made, the government is committed to having an enduring defence presence in Scotland where it continues to invest heavily."
Fort George currently houses soldiers from the Black Watch (3 SCOTS).
Campaigners claim the closure of the base would put 750 jobs at risk and cost the local economy ??16m.
Ms Davidson described the meeting with Mr Lancaster as "very worthwhile".
She added: "It gave us an opportunity to clearly articulate a very sound case for maintaining the last army barracks in the Highlands.
"I hope that the MoD now understands the importance of Fort George to the Highlands and the wider economic impact of removing the base.
"We understand that the review is very long term and I hope that our representations will be taken into account when it comes to making a decision."
Political leaders from the Highlands have expressed disappointment after failing to get reassurances about the future of the Fort George army base.