But the ACT government has demanded the opposition prove its claims that rates will ''triple'' under the reforms, saying the campaign is ''based on a lie''.

The Liberals' ad will be screened across all commercial stations claiming ''Labor or Greens equals triple your rates''. The images of families poring over bills is the latest assault on the 20-year tax reform plan as it becomes the key battleground of the election campaign.

Yesterday marked the official start of the ACT election campaign, with the government now in caretaker mode ahead of the October 20 poll.

Labor leader Katy Gallagher also entered campaign season on the front foot. Today she will promise to spend $30 million on expanding services at the Centenary Hospital for Women and Children if she is re-elected Chief Minister, including funding an extra 19 beds.

The Liberals, led by Zed Seselja, have pinpointed Ms Gallagher's own portfolio of health as an apparent weak point and have already released a series of attack ads on the issue.

But it was taxation policy which dominated much of Wednesday's leaders debate, with Ms Gallagher insisting rates would rise on average by less than $3 a week under the plan.

Mr Seselja said yesterday that Labor was abolishing a range of taxes, including stamp duty, and replacing them with increases to commercial and residential rates and to utilities tax. ''Conveyancing alone is a tax worth $300 million per year,'' he said. ''The utilities tax gets back about $4 million at the most. That leaves $296 million, in today's dollars, that must be replaced through rates. The maths does not add up any other way - if [Treasurer Andrew Barr] drops that much revenue, and says it is going to be replaced with rates - the numbers show that rates must increase by at least three times.''

But government documents show the projected increase in government revenue from residential rates will be less than 10 per cent in the first year of the reforms and less than 30 per cent over the next four years.

The government collected $173 million from residential rates in 2011-12 and that figure is expected to increase by just $16 million in 2012-13 and by $47.7 million by 2015-16. Mr Barr said yesterday that the Liberals were basing their argument on a rates option in the Quinlan review that had not been adopted by the government.

The option gave a 10-year timeframe for the abolition of stamp duty and employed a fixed rates base, rather than the marginal rates system and 20-year reform process the government has introduced.

Under the marginal rates system, the poorest 25 per cent of ACT households will have their rates cut.

Mr Barr said the bulk of the additional rates burden would fall to the commercial sector and not to households.

''Once you exclude the commercial component, the residential part is a very small part of the revenue base,'' he said.

''The only thing that is tripling is the size of Zed Seselja's nose as he continues this campaign of lies.''

But while the budget papers show rates will not triple in the next term of government, Mr Seselja said the budget still ''has rates skyrocketing in the first four years''.

Away from the taxation debate, Ms Gallagher will today announce plans to fund additional beds at the women and children's hospital and an extra 53 nurses, three doctors and allied health and support staff.

The Canberra Sunday Times revealed this week that sections of the new hospital, which opened last month, were already full.

The funding would be rolled out over four years but Ms Gallagher said additional maternity beds would be prioritised to open after Stage 2 of the hospital was completed next year. ''It's progressively rolled out, although I think the maternity beds will be able to be done from the get go,'' Ms Gallagher said.

As well as three new birthing centre/delivery suite beds, funding will be provided for a six-bed maternity assessment unit, four neonatal intensive care beds, five paediatric beds and one foetal medicine unit bed. The $30 million will also include additional funding for outpatient services at the Centenary Hospital and for community-based service. Ms Gallagher said the continuing flight of women from private obstetrics was making it challenging for the public system to keep up with demand.

Labor this week promised to spend $850,000 on a midwife-led birth centre at Calvary Public Hospital.

Ms Gallagher said the Health Directorate was working on new projections for public maternity use and it was likely any further expansion of services would be at Calvary Hospital to help meet the needs of pregnant women in north Canberra.