The federal opposition will attempt to blow a $15 billion hole in the Rudd government's first budget, starting with blocking the controversial alcopops tax.

And Opposition Leader Brendan Nelson has also proposed cutting the petrol excise - a move long opposed by former prime minister John Howard.

Dr Nelson's excise cut would cost $1.8 billion, but is unlikely to go ahead.

He challenged the government to cut petrol tax but stopped short of committing the opposition to introducing its own draft laws in the Senate - which it will control until June 30.

"There is only one way that an Australian government can actually do anything decisive about the price of petrol - and that is to cut taxes," Dr Nelson told parliament in his budget in reply speech.

"So tonight, I propose a cut in fuel excise of five cents a litre."

Dr Nelson said the coalition will use its Senate numbers to reverse the increased excise on ready-to-drink alcoholic beverages, expected to bring in $50 million a month.

The government says the increased excise will deter teenage girls from buying the pre-mixed drinks, known as alcopops, and help battle binge drinking.

But Dr Nelson said the national drug strategy household survey showed binge drinking by young women had actually declined since 2001, a year after the excise was cut.

The budget figures showed the government expected consumption of alcopops to increase by 10 per cent a year despite the excise, he said.

"This is nothing more than a tax binge falsely presented to Australians as a health measure. We will oppose it," he said.

The coalition would also try to stop the government from increasing the annual income threshold for the Medicare surcharge to $100,000, Dr Nelson said.

He said the increase would result in half a million mainly young people dropping out of private health insurance and removing a net $300 million from hospitals.

"We stand up for Australians with private health insurance. We always will. We will oppose this measure."

Dr Nelson, who has been under heavy pressure to bolster his shaky leadership following poor opinion polls, looked nervous throughout his 30-minute speech.

He looked strongest as he attacked the Rudd government for promising to address kitchen table issues like high food prices, rising petrol costs and painful interest rate rises.

"The government has perpetrated a fraud on the Australian public," Dr Nelson said.

"For all his talk of slaying some dragon, the treasurer has breathed new life into inflation with a budget that delivers something Australians have not known in commonwealth budgets for some time - tax increases."

The budget had put tax slugs that would drive up the price of alcohol, cars, groceries, air fares, computer software, canteen meals and health insurance.

He said while inflation had to be managed, the coalition had never called for harsh budget cuts.

"We have never subscribed to the treasurer's assertion that an inflation crisis justifies savage budget cuts at a time of significant domestic and global economic uncertainty," Dr Nelson said.

Before the speech, Prime Minister Kevin Rudd said the opposition had spoken out against $13 billion in budget savings.

With the petrol tax cut, the figure is closer to $15 billion.

"There is a very basic and fundamental challenge for the leader of the opposition tonight, which is to indicate where these savings will be otherwise (found) in the budget," Mr Rudd said.

Opposition treasury spokesman Malcolm Turnbull appeared to steal Dr Nelson's thunder when he ended question time with a futile attempt to censure the government.

Mr Swan accused Mr Turnbull, who missed out on the Liberal leadership to Dr Nelson by three votes last November, of launching a stunt to ambush his leader and get his face on television.

"(He is) the pretender from Point Piper," Mr Swan said.

"This was the speech of an ego that couldn't bear not to be on the television news tonight - somebody who is so out of touch he thinks that we should pay welfare to millionaires".