A free TV licence will only be available to households with someone over 75 who receives pension credit from June next year.
Dame Helen, 73, is one of 20 celebrities – including Sir Lenny Henry, Lionel Blair, Christopher Biggins, Len Goodman and Angela Rippon – who have signed an open letter calling on the government to ensure the funding continues.
She said: “It’s just absolutely heartbreaking that so many older people are going to lose their free licence, when television plays such an important role in their lives.
“In many cases it acts as an important contact with the outside world.
“I would urge all those involved, including the government, to do the right thing and to carry on funding free licences for all over-75s – the cost of which is surely a small price to pay for keeping so many vulnerable older people connected.”
The BBC – which took over the cost of providing the free licences four years ago – announced its plans to scrap the universal benefit last month.
It said continuing to fund the scheme – which amounts to £745m a year – would result in “unprecedented closures”.
And its chairman Sir Davd Clementi has dismissed the suggestion the corporation could fund the benefit by cutting the pay of stars, saying “the sums don’t add up”.
Age UK said it has received around 36,000 letters, which will also be delivered to Conservative HQ, asking Tory leadership hopefuls Jeremy Hunt and Boris Johnson to reconsider the government’s decision to hand responsibility for the funding to the BBC.
It said 83% people surveyed want the government to stick to its manifesto promise to fund free TV licences for over-75s.
Its research shows two in five of all over-75s consider television to be their main form of company, while nine out of 10 in this age group watch TV every day.
Age UK director Caroline Abrahams said: “The government should never have outsourced this welfare entitlement in the first place but the new administration that is about to come into place at least has the opportunity to wipe the slate clean and right the wrong that’s been done to our older population.”
The charity’s online petition has reached more than 600,000 signatures.
MPs are expected to quiz BBC bosses over the proposed changes later.
Mr Clementi and BBC director-general Lord Tony Hall are among those due to appear before the Commons digital, culture, media and sport committee (DCMS).
A government spokesman said: “We’re very disappointed with this decision – we’ve been clear that we want and expect the BBC to continue this concession.
“People across the country value television as a way to stay connected, and we want the BBC to look at further ways to support older people.
“Taxpayers want to see the BBC using its substantial licence fee income in an appropriate way to ensure it delivers for UK audiences, which includes showing restraint on salaries for senior staff.”