WASHINGTON, Sept 15 (Reuters) - The United States, Britain and Australia said on Wednesday they would establish a security partnership for the Indo-Pacific that will involve helping Australia acquire nuclear-powered submarines, as Chinese influence over the region grows. Under the partnership, announced by President Joe Biden, British Prime Minster Boris Johnson and Australian Prime Minister Scott Morrison, the United States will provide Australia with the technology and capability to deploy nuclear-powered submarines. In a three-way virtual announcement from each of their capitals, the leaders stressed that Australia will not be fielding nuclear weapons, but will be using nuclear propulsion systems for the vessels, to guard against future threats. "We all recognize the imperative of ensuring peace and stability in the Indo-Pacific over the long term," said Biden."We need to be able to address both the current strategic environment in the region, and how it may evolve because the future of each of our nations and indeed the world depends on a free and open Indo-Pacific enduring and flourishing in the decades ahead," he said. Morrison said the submarines would be built in Adelaide in close cooperation with the United States and Britain. "We will continue to meet all our nuclear non-proliferation obligations," he said. Johnson called it a momentous decision for Australia to acquire the technology. He said it would make the world safer. EYES ON CHINA The move comes as Washington and its allies are looking for ways to push back against China"s growing power and influence, particularly it"s military buildup, pressure on Taiwan and deployments in the contested South China Sea. The three leaders did not mention China and senior U.S. administration officials who briefed reporters ahead of the announcement said the move was not aimed at countering Beijing. U.S. officials said nuclear propulsion would allow the Australian navy to operate more quietly, for longer periods, and provide deterrence across the Indo-Pacific. The officials said the partnership, dubbed AUKUS, will involve cooperation in areas including artificial intelligence, quantum technology and cyber. The partnership looks likely to end Australia"s negotiations with French shipbuilder Naval Group to build it a new submarine fleet worth $40 billion to replace its more than two-decades-old Collins submarines, Australian media reported. read more"This new architecture is really about deepening cooperation on a range of defense capabilities for the 21st century, and ... these relationships with Great Britain and Australia are time- tested," one of the U.S. officials said. The three countries would launch an 18-month effort involving technical, strategic and navy teams to identify "the best ways for Australia to pursue nuclear-powered submarines," the official said. "This will give Australia the capability for their submarines to basically deploy for a longer period, they"re quieter, they"re much more capable. They will allow us to sustain and to improve deterrence across the Indo-Pacific." The pact should be a boon for the U.S. defense industry and among the firms that could benefit are General Dynamics (GD.N) and Huntington Ingalls Industries (HII.N), which lead the U.S. submarine industrial base, which includes thousands of other companies. General Dynamics" Electric Boat business does much of the design work for U.S. submarines, but critical subsystems such as electronics and nuclear powerplants made by BWX Technologies Inc (BWXT.N) Britain described it as a very significant announcement and said the 18-month program would work out details as to what countries and companies would do what, with the aim is for the first submarine to be delivered as quickly as possible. The U.S. officials who briefed reporters about the deal did not give a time frame for when Australia would deploy a nuclear-powered sub or how many would be built. They said that since Australia does not have any nuclear infrastructure, it would require a sustained effort over years. ONE-OFF TECHNOLOGY SWAP One U.S. official said the announcement was the result of several months of engagements between respective military commands and political leaderships, during which Britain - which recently sent an aircraft carrier to Asia - had indicated it wanted to do more in the region. read more "What we"ve heard in all those conversations is a desire for Great Britain to substantially step up its game in the Indo-Pacific," the official said, noting its historical ties to Asia. The U.S. official said the United States had shared nuclear propulsion technology only once before - with Britain in 1958 - and added: "This technology is extremely sensitive. This is frankly an exception to our policy in many respects, I do not anticipate that this will be undertaken in other circumstances going forward. We view this as a one-off." The move was being taken as part of "a larger constellation of steps" in the region, including stronger bilateral partnerships with long-term allies Japan, South Korea, Thailand and the Philippines, and stronger engagements with new partners like India and Vietnam. The U.S. official said Biden had not mentioned the plans for the trilateral partnership "in any specific terms" to Chinese leader Xi Jinping in a call last Thursday, but the U.S. president did "underscore our determination to play a strong role in the Indo-Pacific." read more The announcement comes just over a week before Biden is to host a first in-person meeting of leaders of the "Quad" group of countries - Australia, India, Japan and the United States - that Washington sees as a key means to stand up to China. read more The Biden administration has declared the Indo-Pacific its key foreign policy focus and the region has seen a series of high profile visits from top U.S. officials, including Vice President Kamala Harris. read more