Ford's engine plant in Bridgend will have opportunities to bid for new work which could secure threatened jobs, the Welsh secretary has said.
A leaked document showed Ford was projecting a reduction of 1,160 workers by 2021 at the plant.
But Alun Cairns said he was optimistic there would be chances "to bid for new engines along the way".
He met Ford earlier this week to discuss the life cycle of its engines and said discussions would continue.
On Wednesday, Ford shared its five-year outlook with unions in the wake of reductions in planned investment in its new Dragon engine.
It said there were "healthy volumes" of work over the next two to three years but that "identified workload is reduced" beyond that.
But Mr Cairns told BBC Wales: "There are some good engines, some very good skills, and I'm determined to do everything I can in order to make those jobs as sustainable as possible over the long-term.
"There will be opportunities to bid for new engines along the way so long as we can make the plant in Bridgend, the plant in Dagenham and complementary industries as efficient as possible."
Later, during a House of Commons debate on Welsh affairs, Mr Cairns told MPs: "We need to recognise that in relation to Ford there is a natural life cycle of a product and I think we need to be realistic in terms of where we were expected to be at this stage of development."
Mr Cairns said Bridgend MP Madeleine Moon had said there were challenges in efficiency and productivity that the unions, plant and government wanted to face.
But he added: "When I met Ford just two days ago there was a recognition that the sustainable future is optimistic but there is the opportunity and the need to win further business for when the natural life cycle of the existing engine ends and it is in that basis that I look positively at the challenges that we face in order to make those jobs sustainable over the longer term."
He was critical of what he said had been the "selective" presentation of some details about the plant's prospects.
'Kick in the teeth'
Mr Cairns has said Nissan's investment in Sunderland since the referendum would boost Wales component companies while he also wanted to help secure jobs at Toyota's engine plant on Deeside, Flintshire.
"This is about making an automotive sector of the highest standard, of the highest quality products in the most efficient way possible," he said.
"I believe as we exit the European Union we can get to the position where these large organisations can drive the agenda and be part of this global Britain."
First Minister Carwyn Jones said on Wednesday the job losses were a "worst case scenario".
Union Unite said it would "use all its might" while the GMB said the outlook, confirmed at a meeting, was a "real kick in the teeth".
Tim Williams, chief executive of the Welsh Automotive Forum, told the BBC's Good Morning Wales programme that "everybody has to work together to secure new products for the plant".
"We have to decide which is the best technology to go into the plant post 2020. We can tackle efficiencies [in Bridgend] if there is an issue there."
He said Brexit was "having an effect" and insisted the UK automotive industry was "looking positive".
But former business secretary Sir Vince Cable said there were "big uncertainties" around Vauxhall's Ellesmere Port and Luton factories and "bits and pieces of the UK car industry are drifting away".
"It would be amazing if Ford weren't going through a similar thought process," he added.
He said he hoped, post-Brexit, UK car companies would be exempt from any removal from the customs union.
"There is also potential the UK government will no longer need approval for state aid.
"But they are not giving the impression they want to make interventions of that kind."