Let the good times roll. That would be the theme song of Scott Morrison's third, and he hopes not last, budget.

A strong rebound in company tax revenue and more people in jobs have boosted tax revenues and the current Treasurer, as have many before him, intends to return some of that bounty to households ahead of a looming election.

It looks likely Labor will join the party, possibly even using revenue raising in other areas to promise a greater income tax return.

But not everyone is buying the "rivers of gold" tax reduction mantra.

ANU economics professor and former Liberal leader John Hewson — who famously lost the "unlosable" 1993 election to Paul Keating because of a GST and spending cut plan called "Fightback" — said the Turnbull Government was making the same mistakes as the Howard government in its latter years.

From the leaks he has seen, he has already labelled 2018 the "mother of all political budgets".

"I suspect there's a bit of a back payment of company tax, a pick-up in commodity prices and a fairly strong growth in employment over the last 12 months or so," Dr Hewson told RN Breakfast.

Sorry, this audio has expired 2018 Budget preview

"Now I don't see on the basis of partial evidence that any of those things is going to be sustained.

"Now they're falling into the Howard-Costello trap of having unexpectedly strong revenue and committing it rather than putting it away for a rainy day."

'Vote-buying exercise' ahead of early election

Dr Hewson is not alone in his worries that the Government is planning to hand back a temporary revenue boom in permanent tax cuts, just as the Howard government did several times during the mining boom.

TD Securities economist Annette Beacher said Mr Morrison and Finance Minister Mathias Cormann had been very vocal in talking up a 23.9 per cent of GDP cap on revenue, but there had been "crashing silence" about having a similar cap on expenditure, which has been around 25-26 per cent of GDP for some time.

Scott Morrison looks set to deliver tax cuts and promise an earlier return to surplus. ( ABC News: Matt Roberts )

"Are we going to see wafer thin surpluses because the Turnbull Government seems to find itself not doing too well in the polls?" she asked rhetorically.

"This to me seems like a purely vote-buying exercise."

Dr Hewson's political instincts tell him that any "vote buying" is a matter of some urgency.

"The prospect of an early election this year I think is very real," he said.

"I see they've [the Liberal Party] cleared the deck for preselections to be settled by June, so I suspect that they could go as early as August/September this year."

Dr Hewson points to elections in the nation's two most populous states — Victoria in November and New South Wales in March 2019 — as making an early election attractive.

The Turnbull Government must go to the polls by May next year at the latest.

However, Dr Hewson believes tax cut largesse by both major parties may backfire as voters start looking for longer-term policies.

"I do think the electorate is tired of these short-term political games," he said.

"One-in-three didn't vote for either major party at the last election, there's a lot of disenchantment with politics, they don't really believe them at face value.

"So I think an honest assessment of where we sit, in today a very risky world both in economic and geopolitical terms, and what challenges we will meet over the next 10-15 years ... I think the electorate is looking for a realistic assessment."

Ratings agencies not worried as debt heads towards $600 billion

Dr Hewson listed a few of those challenges — an aging population, infrastructure requirements, funding the National Disability Insurance Scheme and defence spending — and said none of them are really funded within the budget, with the Government relying on strong future economic growth to pay the bills.

It does so with a significant debt burden, which Annette Beacher said could hit $600 billion in gross terms by the end of the year.

While the budget is still in deficit that debt will keep growing, and Ms Beacher is disappointed the Government is not using recent revenue windfalls to return to bigger surpluses sooner.

"I think the economy's in good shape and I'm really wondering when are we going to start talking about proper budget surpluses that start to pay down debt," she said.

According to Fitch Ratings, Australia's government debt — federal and state combined — has risen from about 19 per cent of GDP in 2010 to 42.1 per cent currently.

Jeremy Zook, who rates Australian governments for Fitch, said that has moved the nation from being the leader among those countries rated AAA to middle of the pack.

But that is not enough for Fitch to consider downgrading the nation's credit rating.

"We just recently affirmed Australia's AAA rating and we have a stable outlook on the rating, which means we don't anticipate any significant likelihood that there will be a downward rating action in the near term," he told RN Breakfast.

Rival ratings agency Moody's agrees.

"The debt burden is fairly modest in relation to its ratings peers and, therefore, it's not necessarily a key issue at this stage," said its analyst who rates Australia, Martin Petch.

However, Standard & Poor's, the one major ratings agency that does have Australia on a negative credit rating watch, declined an invitation to speak with the ABC ahead of the budget.

There is some speculation it may lift that negative watch, but that will depend how sustainable it thinks Treasury's current "rivers of gold" are well into the future.