WASHINGTON -- Senior Pentagon officials on Wednesday sought to defend the use of Russian-made rocket engines to send U.S. military satellites into space, telling exasperated lawmakers they are moving quickly to end the practice and rely on American-made rockets for the launches.

But Air Force Secretary Deborah James and Pentagon acquisition chief Frank Kendall failed to stem criticism from several members of the Senate Armed Services Committee who view Russia as the chief geopolitical threat to the U.S.

Led by the committee chairman, Sen. John McCain, R-Ariz., they said using the Russian engines enriches President Vladimir Putin's inner circle and puts U.S. national security in jeopardy.

McCain, his voice rising at times, asked James and Kendall whether they knew the names Sergey Chemezov and Dmitry Rogozin. Both are Russians targeted by U.S. sanctions, he said, yet their positions in Russia's space and defense industry allows them to personally profit from the sales of the Russian RD-180 engines. Each engine costs roughly $30 million.

"So we now have senior Russian politicians, friends of Vladimir Putin, that are making tens of millions dollars in the pass-through money that is paid for the Russian rocket engines," McCain said. He asked James whether she found that disturbing.

"Yes," James responded, although she said she couldn't be certain whether Russian officials were benefiting directly from the sales.

Disengaging from use of the Russian engines is a priority but more complicated than it appears, James said. She recommended a stockpile of 18 of the RD-180s until an equally capable American-made space launch vehicle can be tested and fielded.

James also said she asked senior Pentagon officials Wednesday to work with other federal agencies to ensure purchase of the engines does not conflict with U.S. sanctions.

The Pentagon has tried to undermine the committee's direction to limit that risk and end the use of the Russian RD-180 engines by the end of this decade, McCain said. He also blamed the U.S. contractor that acquires the engines, United Launch Alliance, and two senators who support the company, Richard Shelby, R-Ala., and Dick Durbin, D-Ill., for thwarting the committee's instructions.