WASHINGTON, Aug 7 (Reuters) - NASA officials said on

Wednesday that the two astronauts delivered to the International

Space Station by Boeing's ( BA ) Starliner could return on

SpaceX's Crew Dragon in February 2025 instead if Starliner is

still deemed unsafe to return to Earth.

The U.S. space agency has been discussing potential plans

with SpaceX to leave two seats empty on an upcoming Crew Dragon

launch for NASA astronauts Butch Wilmore and Suni Williams, who

became the first crew to fly Boeing's ( BA ) Starliner capsule to the

ISS in June.

The astronauts' test mission

, initially expected to last about eight days on the

station, has been drawn out by issues on Starliner's propulsion

system that have called into question the spacecraft's ability

to safely return them to Earth as planned.

Thruster failures during Starliner's initial approach to

the ISS in June and several leaks of helium - used to pressurize

those thrusters - have set Boeing ( BA ) off on a testing campaign to

understand the cause and propose fixes to NASA, which has the

final say.

But the results of those tests have done little to quell

concerns about

Starliner's safety

and stirred disagreements and debate within NASA about

whether to accept risk with Starliner or make the decisive call

to use Crew Dragon instead.

Using a SpaceX craft to return astronauts that Boeing ( BA )

had planned to bring back on Starliner would be a major blow to

an aerospace giant that has struggled for years to compete with

SpaceX and its more experienced Crew Dragon.

Early Tuesday morning, NASA, using a SpaceX rocket and a

Northrop Grumman capsule, delivered a routine shipment of food

and supplies to the station, including extra clothes for Wilmore

and Williams.

Starliner's high-stakes mission is a final test required

before NASA can certify the spacecraft for routine astronaut

flights to and from the ISS. Crew Dragon received NASA approval

for astronaut flights in 2020.

Starliner development, developed under the same NASA

program, has been set back by management issues and scores of

engineering problems. It has cost Boeing ( BA ) $1.6 billion since

2016, including $125 million from Starliner's current test

mission, securities filings show.

CONCERNS AT NASA

A meeting this week of NASA's Commercial Crew Program,

which oversees Starliner, ended with some officials disagreeing

with a plan to accept Boeing's ( BA ) testing data and use Starliner to

bring the astronauts home, officials said during a news

conference.

"We didn't poll in a way that led to a conclusion,"

Commercial Crew Program chief Steve Stich said.

"We heard from a lot of folks that had concerns, and the

decision was not clear," Ken Bowersox, NASA's space operations

chief, added.

A Boeing ( BA ) executive was not made available at the press

conference.

While no decision has been made on using Starliner or

Crew Dragon, NASA has been buying Boeing ( BA ) more time to do more

testing and gather more data to build a better case to trust

Starliner. Sometime next week is when NASA expects to decide,

officials said.

The agency on Tuesday delayed by more than a month

SpaceX's upcoming Crew Dragon mission, a routine flight called

Crew-9, that is expected to send three NASA astronauts and a

Russian cosmonaut to the ISS.

NASA's ISS program chief said the agency has not yet

decided which astronauts they would pull off the mission for

Wilmore and Williams if needed.

Boeing's ( BA ) testing so far has shown that four of

Starliner's jets had failed in June because they overheated and

automatically turned off, while other thrusters re-fired during

tests appeared weaker than normal because of some restriction to

their propellant.

Ground tests in late July at the White Sands Missile

Range in New Mexico have helped reveal that the thrusters'

overheating causes a teflon seal to warp, choking propellant

tubes for the thrusters and thereby weakening their thrust.

"That, I would say, upped the level of discomfort, and

not having a total understanding of the physics of what's

happening," Stich said, describing why NASA now appears more

willing to discuss a Crew Dragon contingency after previously

downplaying such a prospect to reporters.