WASHINGTON, April 9 (Reuters) - President Donald Trump's

nominee to lead NASA, entrepreneur Jared Isaacman, will face

questions from senators on Wednesday about on how to balance

Trump's focus on reaching Mars with the U.S. space agency's

flagship moon program.

Isaacman, CEO of payment processing company Shift4 Payments ( FOUR )

, is a close partner of Elon Musk's SpaceX who has flown

to space twice as a private astronaut on the company's

spacecraft.

The billionaire is in Washington for a confirmation hearing

before the U.S. Senate Committee on Commerce, Science, &

Transportation committee in which conflicting views on the moon

and Mars as a destination for U.S. astronauts will be front and

center.

If confirmed, Isaacman, 42, would oversee 18,000 employees

and a budget of roughly $25 billion focused heavily on returning

astronauts to the moon's surface, as part of a program called

Artemis. Trump started the program during his first term.

But the president and Musk, who spent $250 million in

support of Trump's presidential campaign and pushed for

Isaacman's nomination, have become fixated on Mars as a national

priority, raising questions about NASA's moon program for which

billions of dollars have been committed.

Those views on the Red Planet could complicate Isaacman's

path to confirmation, as he balances intense pressure from

lawmakers and NASA to stay course with the moon program with

pressure from Trump and Musk to get the U.S. to Mars.

"We will prioritize sending American astronauts to Mars,"

Isaacman will say in prepared testimony. "Along the way, we will

inevitably have the capabilities to return to the moon and

determine the scientific, economic, and national security

benefits of maintaining a presence on the lunar surface."

The four astronauts assigned to NASA's Artemis 2 mission -

which involves a flyby of the moon in 2026 before a subsequent

moon landing mission - had front row seats in the hearing.