Cherelle Griner made the plea to the President during a sitdown interview with Robin Roberts on "Good Morning America" this week ... explaining she believes Biden could be the key to getting Brittney back on U.S. soil.

"I just keep hearing that he has the power," Cherelle said of Biden. "She's a political pawn -- so, if they're holding her because they want you to do something, then I want you to do it."

Brittney has been detained in Russia since mid-February ... after authorities claimed they found hash oil in her luggage.

Cherelle told Roberts she initially found out about it all through a panicked, early-hours text message from Brittney.

"She started texting me around 2 AM that morning," Cherelle said. "'Babe! Babe! Babe! Wake up! They have me in this room, I don't know what's going on.'"

Cherelle said Brittney told her the authorities were taking her phone and not to text anymore -- and she said outside of written letters, she has not been able to speak to Brittney since.

Cherelle said she has been in contact with Secretary of State Antony Blinken about ways they can bring home Brittney ... but she clearly feels more can be done by the U.S. government.

"I was grateful for their call," she said of the talk with Blinken. "You say she's top priority, but I want to see it. And I feel like to see it, would be me seeing BG on US soil."

Cherelle added being without Brittney -- who's expected to remain in custody in Russia until at least her next court hearing in June -- has been difficult ... and she even broke down in tears during the interview with Roberts.

She did explain, however, that Brittney has told her to remain strong.