But the department disagrees, arguing measures introduced in the past three years to protect national security and community safety are delivering results.

An Australian National Audit Office review has found just 15 per cent of applications for citizenship "by conferral" - which makes up the bulk of applications - were processed within 80 days in 2017/18.

That compares to the department's former target to process 80 per cent of applications within 80 days, which it dropped in 2017.

The department does, however, measure the time taken to obtain citizenship from lodging an application to attending a ceremony.

The auditor-general found that time "increased significantly" between March 2017 and September 2018, despite a dip in the "relative complexity" of applications being lodged.

"Growth in demand for citizenship in recent years was driven by people with good supporting documents who arrived in Australia on a skilled visa," the audit office found.

The review suggests increased screening of applicants has played a major role in extended processing times.

Nevertheless, it found staff were not being using efficiently.

"The department has a suite of initiatives in train that are designed to enhance efficiency but has been slow in implementing them," the review stated.

The Department of Home Affairs disputes the audit office's claim. In a statement to the auditor-general, it highlighted that the proportion of citizenship applications knocked back has doubled from 3.4 per cent in 2014/15 to 6.8 per cent in the first few months of 2018/19.

That comes as new security measures have been introduced.

"The enhanced integrity measures adopted by the department over the last three years to protect Australia's national security and community safety are delivering results," the department said.

"We will always prioritise these efforts over speed."

The department has agreed to the auditor-general's recommendation to revise how it funds its citizenship activities, based on the latest activity levels.

But the department has knocked back a recommendation to publicly report its key performance indicators, saying they could give people unrealistic expectations.

The inquiry came after the commonwealth ombudsman, Refugee Council of Australia and others raised concerns about the duration of the citizenship application process.

Australian Associated Press