Dozens of top public service jobs at the giant Department of Human Services, paying up to $400,000, are sitting vacant, some for as long as 15 months.

The department has been without a finance boss since October 2013 and two of the seven jobs at its second-top level of management have no permanent occupant.

The jobs are sitting vacant despite the availability of dozens of senior executive-level public servants, who have lost their jobs in other departments but remain on the Commonwealth payroll.

Senior executives at DHS earn annual salaries of between $150,000 and $388,000, which are then topped up with allowances and benefits such as cars.

The list of vacancies at DHS grew last month when senior manager Ben Rimmer, whom the department had touted as a management success story, left just months after returning from a training course at Harvard University, at a cost to taxpayers of $10,000.

The move, to a $450,000 job at Melbourne City Council, leaves no one at the helm of the "service delivery transformation" project in the sprawling department that runs Centrelink, Medicare and the Child Support Agency.

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But DHS bosses said this week the department was hiring, and that 12 new senior executives had been employed in November and December.

Departmental documents show that, of the 192 top jobs in the department, 25 were vacant at January 5, and at least one, the chief financial officer, has been empty since September 2013.

Mr Rimmer had been responsible for 600 staff and the transformation of the department's delivery of services – Centrelink, Child Support and myGov, as well as Medicare – to millions of Australians using digital technology.

The former Department of the Prime Minister and Cabinet executive quit DHS late last year.

Departmental secretary Kathryn Campbell told Labor's human services spokesman Doug Cameron at a Senate estimates hearing in October that she did not think it was unusual that the crucial chief financial officer role should be vacant for more than a year.

A departmental spokeswoman confirmed this week that 16 executive level jobs were vacant.

"Arrangements for some of these positions are currently being considered, and several positions will be filled or advertised shortly," she said.

"There are no current impediments to filling vacancies, with recruitment activity in November and December resulting in the permanent filling of 12 vacant SES positions.

"Some of these recent appointments are not yet reflected in the current organisational chart."

Senator Cameron criticised the failure to fill the vacancies, saying it had the potential to harm the department's customer service performance.

"Not filling key positions is detrimental to service delivery, sound policy development and is further evidence of the government's ideological obsession to outsource and privatise," he said.