Federal Treasurer Wayne Swan will tonight hand down his third budget and the Government is promising it will not be the usual pre-election spend-a-thon.

Tonight's budget is likely to show a path back to surplus sooner than previously predicted with MPs saying the Government's economic credentials matter more than election sweeteners.

But with the Prime Minister's support plummeting in the polls, he has faced some tough questions in Caucus about recent policy back flips.

Kevin Rudd moved to ease some of those tensions last night, rolling out the welcome mat for backbenchers at the Lodge for pre-budget drinks.

Hours earlier they had grilled Mr Rudd in Caucus about recent policy changes on emissions trading and asylum seekers.

Home Affairs Minister Brendan O'Connor says it has been blown out of proportion.

"I think the media played up the so-called angst," he said.

But as they departed for the lodge, some backbenchers acknowledged it was a lively discussion.

"Lots of people asked questions and they were neither hard nor soft and it is a Caucus," Braddon MP Sid Sidebottom said.

One backbencher told AM the Government is going through some "stormy weather" and the Prime Minister did nothing to ease the fears of marginal seat holders.

Others said Mr Rudd responded well to the questions and the mood was more jovial than expected.

Another backbencher said the drinks at the Lodge should not been seen as a response to the recent plunge in the polls, or as reflective of the need to keep nervous backbenchers on side.

Mr O'Connor says the message from Caucus is clear.

"I think the Prime Minister emphasised this to remind the Australian people that we confronted the greatest economic challenge of our lifetime with the global financial crisis and we came out of that global financial crisis the best performing economy and that has taken up a large part of the Government's time," he said.

Budget spending

The Government has played down expectations of a pre-election spending spree in tonight's budget, but health will be one area to get a funding boost.

Carol Bennett from the Consumers Health Forum says they will be looking for the budget to add to the deal agreed at last month's COAG meeting with the states and territories.

"While we appreciate the extra money that is going into hospitals that the Prime Minister has announced already, we are hoping that this budget will deliver some out-of-hospital services that will keep people out of hospital," she said.

"So... extra primary care, GP, community services."

But with the Treasurer vowing that his budget will be "no frills", some areas will miss out.

Mental health advocates have been disappointed with the Government's health plans so far.

The Mental Health Council's David Crosbie says he is not optimistic about the budget.

"Well, I'd hope mental health isn't seen as a frill," he said.

"I think mental health is very much a special case where we have under-invested really for decades and we are now paying a huge price for that.

"If we don't invest more, particularly at a community level, we will continue to pay a huge price for mental health care, usually through our hospitals, but also through our police, our courts, our ambulances, our prisons and our homeless shelters, many of whom are picking up people who have fallen through the gaps of our health system."

Surprise spending?

There is speculation Mr Swan might have another big ticket item to woo voters, but Opposition finance spokesman Andrew Robb says that would be foolish.

"If they don't tackle the reckless spending and the huge debt hanging over our economy then they have missed the point, they have failed," he said.

Mr Robb says the Government should be cutting spending rather than relying on taxes to improve the budget bottom line.

"Their answer so far is simply to ramp up taxes or introduce new ones," he said.

"They have got to get down and live within their means like the average family has to in their circumstance."

Greens Leader Bob Brown says he will be watching the budget to see how the Government uses the money saved from the decision to delay the emissions trading scheme.

"The money the Government may save shouldn't be going to consolidated revenue. It should be going into fostering renewable energy, energy efficiency, and clean, fast, efficient public transport," he said.

Senator Brown says he wants Labor to add to the billions of dollars already promised for the health system by funding universal dental care as well.

"It's expensive not to have a universal dental health care system," he said.