David Cameron said it was "fair" to protect the basic state pension from cuts, but declined to rule out a squeeze on other pensioner benefits after the general election.
The Prime Minister has pledged to retain the "triple lock" guarantee of minimum annual pension rises of 2.5% until at at least 2020 if the Tories win the next election.
He said that it was right to prioritise "dignity and security" for people in their old age while austerity continued to bite into welfare and other spending.
But he failed to carry over a pledge made for the duration of this parliament to continue winter fuel payments, free prescriptions, bus passes and TV licences for all pensioners.
"I made a very clear promise. We've kept that promise," he said - amid mounting political pressure from all sides to remove such perks from better-off OAPs.
"We will set out our plans at the next election in our manifesto."
Labour has said it would strip winter fuel payments from the richest 5% of pensioners and the Liberal Democrats have also said they would means-test the benefits.
Under the "triple lock" the basic state pension rises in line with inflation, wages or 2.5% - whichever is the highest.
Mr Cameron said the protection had been made possible by "difficult decisions" such as extending the retirement age, meaning millions in their 30s and 40s will wait longer to get a pension.
"Politics is about choices and the choice I make is: yes, we should be giving pensioners dignity and security in their old age," he told BBC1's Andrew Marr Show.
"It is fair because you should be protecting pensioners," he added - insisting the Government was also taking a series of actions to improve conditions for young workers.
Labour leader Ed Miliband said the Opposition would hold back from making tax and spending commitments until it published its election manifesto.
"But nobody should be in any doubt about our commitment to the triple lock," he added.
Deputy Commons Leader Tom Brake indicated that he expected the Liberal Democrats to match the extension of the guarantee - which was originally in the party's 2010 manifesto.
"I am very pleased that the Prime Minister is underlining his support for what is a Liberal Democrat policy," he told Pienaar's Politics on BBC Radio 5 Live.
"What I can't do this morning is pre-empt what our manifesto process is going to agree. But I suspect the 'triple lock' may well feature prominently."
Mr Cameron has already indicated that the state pension would be the only spending exempt from a new cap on overall welfare spending.
Labour had excluded it "in the short term", Mr Miliband said.
"Obviously in the longer term we've got to keep an eye on these things - the long-term forecasts for pensions."
The Labour leader accused Mr Cameron of planning another "tax cut for millionaires" after the Prime Minister declined to rule out a further cut in the top rate of income tax.
"He wants further tax cuts for the richest in society at a time when ordinary families are facing a cost of living crisis," he declared.
Mr Cameron insisted, though, that his priority was reducing the burden on the lowest earners.
He said reducing the top rate from 50p to 45p rate was set to "bring in better percentage" to the Treasury and that he was open to suggestions for how to maximise revenues.
"I actually want the rich to pay more so you ought to set tax rates that encourage people to earn, to set up businesses, to make money and then to pay taxes," he said.
"We will set taxes to raise revenue ... not to make a political point.
"But if I had some money in the coffers I would target that money at the lowest paid, at those who work hard, who want to get on.
"Those are the ones that need our help."
Mr Cameron said the job of the Government was "not even halfway done" as he played down opinion polls giving Labour a consistent lead.
The latest large-scale survey by f ormer Conservative Party deputy chairman Lord Ashcroft also painted a gloomy picture of the chances of securing an overall Tory majority in 2015.
It found that more than one in three people who voted Tory in the 2010 general election are not presently planning to do so next time - with half switching allegiance to the UK Independence Party, a fifth aligning themselves with Labour or the Liberal Democrats and a third undecided.
But in a more hopeful sign, a clear majority of those "defectors" (56%) think David Cameron is the best of the three main party leaders and say their preferred outcome in 2015 would be a Conservative majority - with Labour struggling to convince voters as an alternative.
"We have a long-term economic plan that we are working to. The plan is working: we have over a million more people in work, we've got 400,000 new businesses operating in Britain, we are one of the fastest-growing countries now in the western world," Mr Cameron told the Marr Show.
"But we can't be complacent. The job isn't even halfway done.
"This year, for me, is a year about governing, it's about delivering. I'm content that the public will judge me and the Government I run and the party I run in 2015.
"But the public need to know that the Opposition are committed to undoing all that good work. It would be like handing back the keys to the people who crashed the car in the first place."