In an attempt to end damaging speculation about the government's plans on superannuation, Treasurer Wayne Swan revealed a ''modest'' package that would deliver $900 million over the four-year budget cycle - well short of the savings needed to cover multibillion-dollar school and disability programs.

If implemented, about 16,000 Australians with more than $2 million in super would lose some tax concessions, while 59,000 people on the top marginal tax rate would have a larger tax liability due to a new interest charge on excess contributions.

But the government appears unlikely to legislate the package before Parliament rises, with Mr Swan signalling the government would take the plans to the election in September.

In bowing to pressure to reveal its hand five weeks before the budget in May, the government has spared itself a negative advertising campaign similar to the mining industry's blitz in 2010 against the resources tax that helped bring down prime minister Kevin Rudd.

Financial Services Council chief executive John Brogden said the group had shelved its planned advertisements for now but warned it could campaign against negative changes to superannuation in the future.

The Coalition denounced the package as an ''attack'' on retirement savings, claiming Mr Swan's reluctance to legislate the changes before the election showed he was not confident of securing caucus support.

But opposition superannuation spokesman Mathias Cormann backed several of the changes, including increasing the amount people could contribute to their super accounts before having to pay more tax.

Mr Swan said Australians on average wages should no longer provide ''excessive support to people with millions in their superannuation account''.

Former Labor prime minister and the architect of the superannuation system, Paul Keating, said the package struck a reasonable balance and helped correct ''unsustainably generous'' changes introduced by former treasurer Peter Costello.

But some groups accused the government of not going far enough in curtailing the ballooning cost of tax concessions on super. The government wants to revoke the tax-free status of earnings above $100,000 a year from super funds that have moved into their distribution phase. Instead, such earnings would attract a 15 per cent rate, the same that applies in the accumulation phase.

Assuming annual earnings of 5 per cent, Treasury predicted the move would affect only individuals who had amassed more than $2 million in their superannuation funds, or 0.4 per cent of retirees, netting the government $350 million over the four-year budget cycle.

The government abandoned a plan to double the cap on concessional superannuation contributions to $50,000 for those with balances of less than $500,000. The cap limits the amount that can be added to super accounts before penalty taxes apply. Instead of lifting the cap of $25,000 to $50,000 for some, the government plans to increase it to $35,000 across the board, starting this July for over-60s and in mid-2014 for over-50s.

Superannuation Minister Bill Shorten said the government had listened to industry feedback that the original proposal would be ''too clunky''.

The cap changes are predicted to save $365 million over four years, the single biggest saving of all the measures.

Concessional contributions in excess of the annual cap are now taxed at the top marginal rate of 46.5 per cent rather than the usual rate of 15 per cent, penalising those on lower incomes who have managed to put extra aside.

The government plans to tax excess concessional contributions at the individual's marginal tax rate, plus an interest charge, costing the budget $55 million over four years. It estimates this will reduce the tax liability of 41,000 people next financial year by an average of $1300 but 59,000 people on the top marginal tax rate will pay more.

With Clancy Yeates and Jacqueline Maley