Treasurer Wayne Swan described Rudd as "honourable" after media speculation pointed to the former leader over damning allegations against his replacement, Julia Gillard.
"I do believe that he's an honourable person," Swan told public broadcaster ABC late on Wednesday.
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"I do believe that he is doing everything that he possibly can to see the return of the government, including campaigning in his local electorate."
Meanwhile Rudd, who is refusing to address national issues as he campaigns in his electorate in Queensland state, rejected any involvement via a statement issued by his spokesman.
"Mr. Rudd remains committed to the re-election of the government," the spokesman said.
However, the Labor Party is reportedly deeply worried by the latest in a series of breaches, and worried about any recurrences in the final stages of a tightening race for August 21 polls.
The welfare leak follows allegations that Gillard reneged on a secret deal to let Rudd remain as prime minister until October, and a story which accused the ex-leader of not attending top-level security meetings.
"What's next?" an insider told the Australian Financial Review newspaper. "We could die the death of a thousand drips."
Rudd was sensationally axed in a party coup in late June, after his sharp fall from record popularity raised jitters about Labor's re-election prospects.
But the latest Newspoll shows centre-left Labor just four percentage points ahead of the conservative Coalition, the same gap as immediately before Rudd's dismissal.
A Morgan poll showed Gillard's personal approval dropping to level with Coalition leader Tony Abbott, while sportsbet.com.au said 90 percent of wagers since late Tuesday were for an opposition win.
Treasurer Swan said he would not speculate on the source of the leaks and would not say if he was investigating who was responsible.
"I don't buy conspiracy theories," he said. "I believe Kevin is well motivated and I also believe he's an important part of our team."
But the opposition seized on the tip-offs as a sign of disunity in the government, now flirting with an electoral defeat which would have been unthinkable just months ago.
"The institute of cabinet and the need for unity and the need for discipline is fundamental to stable government in our system," said opposition frontbencher Andrew Robb.
"This government has not only lost its way, it's now off the tracks and it's heading for a train wreck."
