This time it’s ALL OUT WAR in custody battle brewing between BRISTOL PALIN & LEVI JOHNSTON!

BRISTOL PALIN’s baby daddy Levi Johnston is pushing for full custody of their 3-year-old son Tripp after the preschooler shouted an obscenity on his mom’s new reality show.

What’s worse, the 21-year-old single mom laughed about it and admitted she was doing “a terrible job” disci­plining the little boy.

In response, former “Playgirl” cover boy Levi called Bristol’s parenting skills “terrible” and claimed in a statement that his son would con­tinue “on a downward spiral” if he remains in her care.

“I want full custody of Tripp,” Levi said. “His room is already set up in my house and just waiting for him.”

To bolster his custody case, Levi, 22, plans to use video from Bristol’s new show, “Bristol Palin: Life’s a Tripp,” as evidence that she’s a “terrible parent.”

During a recent episode, Tripp threw a temper tantrum when he was told he couldn’t go to the pool. When Tripp’s 18-year-old aunt Willow tried to calm him, Tripp screamed: “Go away, you (bleep)!” Bristol later apologized for the profanity on her blog, saying he’d picked up the colorful language from “(adult) cous­ins and their friends” and from her father Todd’s “snow-machine buddies.”

Levi – who is expecting a baby girl with fiancee Sunny Oglesby in the next few weeks – is trying to get a court date set before Bristol leaves for Los Angeles to compete on the All-Stars edition of “Dancing with the Stars” in September.

“Levi and Sunny both believe they can give Tripp a more stable en­vironment than Bristol and her family,” added the source. “And they think Tripp’s going to be a great big brother to their little girl.”