PM standing by defence minister

Defence Minister David Johnston is resisting calls for his resignation, including those from his own side.

While Prime Minister Tony Abbott is standing by Senator Johnston for a "rhetorical flourish" denigrating South Australian shipbuilder ASC, the state's Liberal leader is not nearly as forgiving.

"Unless he can rebuild some connection, some rapport, some confidence within the industry, then I don't think he has any alternative (but to resign)," Steven Marshall told reporters.

The minister was also the subject of a censure motion in the Senate on Wednesday after the government used its numbers in the lower house to thwart a similar move by Labor.

Senator Johnston, already the subject of speculation about his future in a possible reshuffle of the ministry, still has the support of the prime minister.

Mr Abbott defended his minister in parliament, saying he was doing an outstanding job.

"I trust (him) ... to deliver us a competent, professional and effective armed force," he said.

Mr Abbott put Senator Johnston's comment that he wouldn't trust ASC to build a canoe - let alone Australia's next fleet of submarines - down to a "rhetorical flourish" during a slip of the tongue.

"He said something in the Senate which he shouldn't have said, which he didn't mean, which he's withdrawn and which he's apologised for," the prime minister said.

Senator Johnston told parliament he regretted making the comments but stopped short of apologising to ASC and its workers.

"This morning, I took my medicine for an hour," he said of Labor attacks on him.

Asked about Mr Marshall's comments, the minister said: "Steven Marshall is a very fine man and should be the premier of South Australia."

Earlier, Christopher Pyne repeatedly side-stepped questions about his cabinet colleague.

"It's not for me to indicate my preferences for who should be in the cabinet," the South Australian said.

Attorney-General George Brandis was more forthcoming, saying Senator Johnston was the best defence minister Australia had seen for some time.

"Each and every one of the senators in this chamber would have said something in one moment of exuberance, which they regret," he said.

South Australian Senator Penny Wong accused Senator Johnston of showing "demonstrable bias" against the ASC and was walking away from his election promise to build 12 new submarines at the corporation's headquarters in SA.

"He is an utter disgrace," she told parliament.

Labor frontbencher Stephen Conroy said the minister's "outrageous" comment posed a threat to national security.

Trade unions have also called for the minister's sacking.

"We would expect most governments should talk up their industries. This government has been talking it down," ACTU secretary Dave Oliver said.