While the scheme was originally promised to be delivered to all Australians with a permanent and severe disability, it seems funding for places was capped at the 5075 "target" built into the original deal between the ACT and federal governments; a figure reached at the end of last month.

But federal minister Christian Porter has said the extra funding would be subject to negotiations after the Territory election, despite the ACT government saying the original agreement left responsibility for the extra places with the Commonwealth.

New applicants may be forced to wait for current scheme participants to die before they can be given support, unless a new deal can be reached to open it up to all those promised support.

Many stakeholders believe the target number in the agreement significantly underestimated the demand for services, with a previous figure closer to 6400, and some believe there could be up to 2000 people in Canberra who could miss out on support.

The National Disability Insurance Agency emailed several organisations in the past fortnight saying that "further agreement between governments is required on the full-scheme funding arrangements, including for additional participants".

People with Disabilities ACT campaign manager Craig Wallace said the organisation was appalled by the decision to "cap new entrants" to the scheme, and that people who had applied "months ago" had had their appointments delayed due to "widespread administrative problems".

"This takes us back to the old state-federal game playing that was a hallmark of the old system and I would go as far as to say that this is dishonest and unconscionable," Mr Wallace said.

"People were told there was no difference when they applied and were encouraged to enter the scheme because it was not meant to be based on funding.

"We were never told it would be operating on a triage basis, and I think there's potentially human rights issues at stake."

Mr Wallace said he believed the ACT government was working hard to remedy the situation, but he held federal minister for social services, Mr Porter, "morally and politically accountable".

"They need to actually deliver the NDIS on time and in full, this is the one promise that actually survived the election, and while I wouldn't go as far as to call for what I might call for, his position would be untenable if this is not resolved," he said.

But Mr Porter said the ACT government had provided the original 5075 figure, "notwithstanding they were aware of larger estimates provided by the Australian government actuary in 2012".

He said the program was not "capped" and that the financial impacts of any additional entrants "will need to be negotiated with the ACT after their election".

But ACT Community Services Directorate director-general Michael De'Ath said the agreement signed in 2012 included "the clear understanding that the Commonwealth government accepts the full cost for any participants beyond" the 5075 figure.

He said the directorate took immediate action to clarify the issue with the Commonwealth once the government was aware of the situation.

"The primary concern for CSD is to ensure all eligible people in the ACT have access to the NDIS," he said.

But Dr Ken Baker from National Disability Services ACT said there were two risks for those hoping to be participants, "if this drags on".

"One, is the people who currently get services through the ACT government won't get the services because the funding will have ended and the organisations don't have the capacity to provide the services without the funding," he said.

"The other, is that new eligible people will be placed on a waiting list without a timeframe, without a plan and without any support."

ACT Disability, Aged and Carer Advocacy Service chief executive Fiona May said she was "horrified" by situation and many of the service's clients were now "in limbo".

"We're still compiling the numbers, but it's at least 50 of our clients who could miss out and growing – it's likely many, many more than that as we are only one provider," she said.

"We've seen considerable administrative delays in processing applications, and bungling of administrative processes in the agency and we've received reports of even some people who submitted applications that were then lost by the agency."

Ms May also urged people to keep applying if they needed support as their applications would still be assessed.