All army personnel were awarded a 2.8% increase this year
The junior ranks of the armed forces should get an immediate £6,000 pay rise to help boost morale, the Lib Dems say.
It was "shameful" that many privates on their first tour of duty earned less than police constables and junior firefighters, leader Nick Clegg said.
He said the move, costing about £300m, could be part funded by cutting 10,000 "desk" jobs at the Ministry of Defence.
Ministers said pay rises for the armed forces had been among the best in the public sector in the past three years.
All military personnel were awarded a 2.8% pay rise earlier this year after the government accepted the recommendations of the Armed Forces Pay Review Body (AFPRB).
As a result, the basic pay of a private on operations rose to between £16,681 and £25,887.
But opposition parties have continued to press for higher pay and better accommodation to reflect the armed forces continuous involvement in conflicts in Iraq and Afghanistan since 2003.
The Lib Dems said there was "widespread dissatisfaction" about pay levels among the lowest ranks. They propose a £6,000 increase in basic pay for entry-level privates in the Army and their equivalents in the other services.
We should now give ordinary soldiers, who are fighting day in day out for us, in our name, the same starting salary as anyone who starts in the fire service or the police service
Nick Clegg, Lib Dem leader
This, they claim, would lift the annual salary of the lowest-paid privates from £16,681 to £22,680.
They are also calling for longer-serving privates and lance corporals to get a £3,000 rise, which would take their average annual pay up to about £25,000.
Corporals, sergeants and higher NCO ranks should get a £1,000 increase, equivalent to an extra £20 a week.
Mr Clegg told the BBC: "I think it's a scandal that we're asking young men and young women to serve in the armed forces, risk their lives on our behalf on the front line and we're not giving them a decent wage.
"That is why I believe we should now give ordinary soldiers, who are fighting day in day out for us, in our name, the same starting salary as anyone who starts in the fire service or the police service."
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The party says salary increases can be paid for from savings within the Ministry of Defence's existing budget, primarily from job cuts.
It is "ridiculous" that the MoD employed one "desk-based" employee for every two serving members of personnel, it argues, and the department could make do with 10,000 fewer civilian employees it deems "non-essential".
A Ministry of Defence spokesman said pay recommendations came from the independent AFPRB and in February it had accepted a pay rise of 2.8% for all serving personnel - among the best in the public sector.
"On top of basic pay, personnel deployed in Afghanistan for a six-month tour receive a tax-free operational allowance worth an additional £2,380 and a Longer Separation Allowance worth at least £1,194," he said.
An Army private on operations would also get a minimum of £1,194 in Longer Separation Allowance and £2,380 tax-free Operational Allowance over a six-month tour, he said.
That pushed the minimum pay for a Private soldier on their first operation up to at least £20,255, he added.