Yeah...this should be for keeps--and why can't gay marry?

BRITNEY SPEARS is going for it one more time, baby! ET has confirmed that Britney is engaged to backup dancer KEVIN FEDERLINE. Yes, the 22-year-old is ready to walk down the aisle again, but this time she's apparently going to take a more traditional route.

Her 55-hour Las Vegas marriage to childhood friend JASON ALEXANDER back in January ended in an annulment. And Federline has been by Britney's side consistently as she recovers from arthroscopic surgery on her knee, which forced her to cancel the remainder of her Onyx Hotel Tour. Marrying Federline will also make Britney a step-mom -- he has a 2-year-old with actress SHAR JACKSON, who's also currently pregnant with his second child.

And they worry that gays disrespect marriage?