Coalition ministers traded blows earlier this week after Work and Pensions Secretary Iain Duncan Smith said he would "encourage" people to forego perks such as free TV licences and winter fuel payments.
Mr Duncan Smith later clarified his comments, saying it was up to pensioners what they do with the money.
But amid calls for "inter-generational fairness", Ms Harman admitted that Labour would look at the policy of universal benefits for pensioners.
She told BBC Radio 4's Today programme: "There's a problem with pensions when you means test. We wanted to tackle pensioner poverty, but things change. You always have to look at everything to make sure that your provision is right for the demography, for the income distribution at the time, there's no mystery about that.
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Ms Harman also admitted Labour would temporarily borrow more if elected to Government.
"Two parts of our five-point plan would involve a reduction in VAT on a temporary basis which would involve a temporary increase in borrowing," she said.
"For part of our programme it would need to be financed by a temporary increase in borrowing for temporary measures. Some of it we have showed how we could pay for it - through for example cutting tax relief on pensions - some of it we've thought would be self-financing, others would require initial borrowing."
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