The two began dating a few months ago, after Spears' 57-hour marriage to childhood friend Jason Alexander in Las Vegas in January. That marriage was annulled within days.
Us Weekly senior editor Caroline Schaefer tells The Early Show co-anchor Rene Syler that although the news came as a surprise, she does think Spears is in love.
Schaefer says, "She's going into this with as much serious thought as she knows how. She's only 22. She's very, very young. But I think she's committed to doing this right now. I think she's really in love with him"
The engagement came as a surprise because Spears, who had known Jason Alexander since she was a child, just started dating Federline about 10 weeks ago, Schaefer says.
Federline was previously involved with actress Shar Jackson of TV's "Moesha." They have a 2-year-old daughter together and are expecting another baby in July.
Schaefer notes, "I think she really does like this guy. She's always said she wants to be a young mom. She wants to get married early. She's ready. She's nesting right now. She just got a puppy. They're house hunting. I think she's looking for the next phase of her life."
Reportedly, Spears mother has given the couple the blessing on the marriage, says Schaefer. "Last time, when she married Jason Alexander, she flew to Vegas and was on Britney watch 24/7; she didn't let her out of her sight for a month. As soon as Brittney goes out of her sight, she goes to Europe and has this whirlwind romance with Kevin."
Now, Schaeffer says, is pretty much resigned to the fact that her daughter's going to do what she's going to do.
Spears, 22, and Federline, 26, have not yet set a date. "There are rumors, but nothing's been confirmed yet," Schaefer says. "It will probably be later this year but who knows? Right now, with Britney, anything's unpredictable."
But Schaefer predicts the wedding will be a big blow-out. "I think she wants a nice, big wedding. What girl doesn't?"
Spears does have lots of time to plan a wedding. She recently canceled her summer tour because of a knee injury she suffered during a video shoot.
Says Schaefer, "She had knee surgery and she has a brace that she'll have to wear for the next month and then, she'll be another eight weeks of rehab and she' is not going to be performing for quite a while."
Spears latest album, "In the Zone," was released in November and has sold more than 2.6 million copies.
Federline appeared in the movie "You Got Served" and performed as a backup dancer for singer Justin Timberlake, Spears' former boyfriend.