A merger between the nation's peak science and IT organisations could result in the loss of about 200 jobs, a Senate estimates hearing in Canberra has been told.

The CSIRO and National ICT Australia (NICTA) are in negotiations to form one body after cuts were announced in the federal budget.

CSIRO chief executive Larry Marshall said the proposed merger was very close, but not finalised.

"The proposal on the table is to join the digital productivity team with the NICTA team and appoint a new chief executive, who we have been recruiting through an external process with the NICTA board," he said.

"And have it essentially run as part of CSIRO, but as a separate company for a team therefore it would have a CEO and a board but it would in a sense be part of CSIRO.

"At some point in the future, possibly in a year or more, merge it in to CSIRO."

The total number of staff at NICTA is 617, however as funding for the body was due to expire in June 2016 their future was in doubt.

Officials say the worst case scenario was for the loss of 200 jobs, but efforts were being made to transfer NICTA employees to CSIRO roles where appropriate.

CSIRO's Dave Williams told the hearing, many of the jobs lost would be backroom support staff.

"We are at a very delicate stage in the discussions because the merger's not complete, and NICTA's not part of CSIRO at the moment, so it's a little difficult to talk about specifics," he said.

"But the situation is that over the next 12 months they'll lose about 25 per cent of the total budgets of the two entities, and that could translate in the worst case into over 200 people."

Dr Marshall said negotiations were continuing to save as many jobs as possible from both organisations.

"If the merger goes ahead then obviously there will be way, way fewer job losses than if it doesn't, because the company (NICTA) will run out of money in the middle of next year," he said.

A decision on whether NICTA would have separate branding from CSIRO was still to be determined.