Ray Rice -- My Window For NFL Comeback Is Closing

Ray Rice knows the clock is ticking on his NFL comeback ... but says if the window closes, he's ready to move on.

Rice hasn't played a down in the NFL since 2013 -- after the ex-Baltimore Ravens running back attacked his then-fiancee in an elevator in an Atlantic City casino.

The 29-year-old has been training like a maniac in the hopes of getting a second chance -- but no teams have pulled trigger ... and Rice knows his comeback chances get worse every day.

"I know that the window for playing is closing," Rice told NJ Advance Media ... "But if my window closes, I'm going to make sure I open up a thousand more opportunities for kids, to give them an opportunity to pick up where I left off."

Rice says he's still training -- "but I'm more training for life."

"I think it's safe to say that football ... I don't want to ever say I'm giving up, because that's never going to be me ... I'm happy."

"I'm in the best shape of my life, and I know if it doesn't happen this year, it's probably something I have to deal with. But you know what? It's not the end of my life."

We got video of Rice training last year -- he still looks like he's in pretty good shape.