NATIONAL HARBOR, Md. — United Launch Alliance, which launches nearly all U.S. government satellites, and secretive rocket-making startup Blue Origin will announce a strategic partnership in rocket engine development at a Sept. 17 event in Washington, a source said Sept. 16.

The announcement will be made at the National Press Club by Jeff Bezos, founder of Amazon.com and Blue Origin, and ULA Chief Executive Tory Bruno, the source said.

The companies announced late in the afternoon of Sept. 16 that Bezos and Bruno would be making an unspecified joint announcement at 12:30 p.m. local time.

The source, who spoke on condition of anonymity, said the announcement would position ULA to develop an engine with Blue Origin to potentially replace the Russian-made RD-180, which currently powers ULA’s workhorse Atlas 5 rocket but faces an uncertain future as tensions with Russia rise.

The move would automatically insert a second dynamic personality from the dot-com world into the national security launch debate. Bezos would effectively join ULA’s side in a fierce battle against Elon Musk’s Space Exploration Technologies Corp., which has been fighting for a share of Pentagon business with a rocket dubbed the Falcon 9.

News of a ULA-Blue Origin propulsion partnership follows a report in the Wall Street Journal that Blue Origin is part of Boeing’s bid to launch crew to the international space station. NASA is expected to announce the winners of its commercial crew competition the afternoon of Sept. 16. Boeing, one of at least three companies bidding for NASA’s Commercial Crew Transportation Capability contracts, has proposed launching its CST-100 capsule atop a ULA Atlas 5 rocket.

ULA has been searching for a new engine after increased pressure from lawmakers and Air Force officials about the RD-180 engine, built by NPO Energomash of Russia and sold to ULA by RD-Amross, a joint venture between Energomash and United Technologies Corp.

Dmitry Rogozin, the deputy prime minister of Russia, who oversees the country’s space sector, has threatened to ban the sale of the engines to the United States for military use, although Air Force and ULA officials have seen no signs of a ban.

Blue Origin, the Kent, Washington, firm bankrolled by Bezos, has told industry and government officials privately that the Air Force should consider a liquid-oxygen/methane engine.

In June, Michael Gass, the former ULA chief executive, announced it had signed “multiple” contracts with unidentified companies to study potential replacements for the RD-180, and hopes to select a single concept for development this year. Among those companies, sources have said, is Aerojet Rocketdyne. The Sacramento, California-based company is the dominant U.S. supplier of large liquid-fueled rocket engines.

The selected companies were asked to study technical feasibility of hydrocarbon-fueled engine concepts, and lay out schedules along with cost estimates and technical risks, Gass said.

Aerojet Rocketdyne has been pushing a kerosene-fueled, 500,000-pound-thrust concept dubbed AR-1, which the company says could be fully developed in four years for less than $1 billion.