BBC Trust chair Lord Patten's vision for S4C
The chair of the BBC Trust says he wants to see a "sensible and effective partnership" between BBC Wales and S4C.
Lord Patten says he wants a "creatively independent" S4C when the BBC takes responsibility for its funding.
He also said he wants to strengthen the Welsh language and emphasised the BBC's role in protecting the "civic space" in national life.
His priority was to steer the BBC through a "challenging" time when it is facing cuts of 20%, he added.
From 2013, S4C will be funded from part of the BBC licence fee, following a decision by the UK government.
The future funding arrangement sparked questions about S4C's independence and claims by the Commons' Culture, Media and Sport Select Committee that the arrangement was a "shotgun marriage".
Speaking about S4C on BBC Radio Wales, Lord Patten, who took over as BBC Trust chairman last month, said he was not in the business of "trying to undermine other peoples' independence".
"I'm in the business of defending the BBC's independence," he told Good Morning Wales.
"It would be ridiculous for me to be in any other position. I want to see a creatively independent S4C.
"Because I'm responsible for licence fee payers' money, obviously we want to be in a sensible and effective partnership with S4C.
"It doesn't get all its money and won't get all its money from the licence fee payer - it also raises money itself.
"My principal priority in the short term is to work with and not over S4C to produce even better programmes."
Lord Patten said that in the medium and longer terms he wanted to debate how to "protect and strengthen the Welsh language," saying it was very important to give "greater prominence to local, regional, national, cultural norms".
He said he was sure a partnership could be developed "which underlines absolutely, unequivocally the independence of S4C".
On Tuesday Lord Patten met First Minister Carwyn Jones, who raised concerns about S4C.
After the meeting, Mr Jones said: "It is essential that the editorial and operational independence of the channel continues and its funding is put on a long-term, secure footing.
"And we also believe that there should be a fundamental review of S4C in order to inform the shape of the channel in the future."
Mr Jones also raised concerns over proposed 20% cuts to BBC Wales, some of which were detailed in a recently-leaked report.
Unions and politicians have responded to the document, which proposes dropping BBC Wales' current affairs programme Week In Week Out and, among other ideas, suggests scaling back coverage of the National Eisteddfod and Royal Welsh Show.
The corporation-wide cost-cutting exercise - called Delivering Quality First - stems from a decision last autumn to freeze the BBC licence fee.
Speaking on the subject, Lord Patten said: "We are very aware of the news coverage of journalism in Wales as well as creative programming in Wales but we have to live within a licence fee which will give us 20% less money by 2016 ."
He added: "I don't think to make the BBC more efficient necessarily means that you have to impact on the quality of the broadcasting".
BBC Wales director Keith Jones has previously said no final decisions are expected "until much later this year and that final recommendations will need the approval of the BBC Trust".
Language campaigners and union members held a lobby outside Mr Patten's meeting with AMs and S4C chair Huw Jones in Cardiff Bay on Wednesday evening.
Bethan Williams, chair of Cymdeithas yr Iaith Gymraeg [the Welsh Language Society], said the BBC refused to answer "fundamental questions regarding S4C".
"With the cuts faced by BBC Wales on top of everything else Welsh broadcasting faces a very dark future," she said.
"We will co-operate with the unions and tens of thousands of people across the country who are opposed to these unwise plans that will affect both S4C and BBC Wales."