Steve Nash to Judge -- I Have NO PLANS to Retire

39-year-old Steve Nash swore under penalty of perjury ... the Los Angeles Lakers star has no plans to hang up his jersey and retire from basketball, TMZ has learned.

The revelation ironically came in the middle of a legal war he's having with his ex-wife over her plans to move with their kids from Arizona to California.

Steve is trying to block the move ... his ex believes it's because Nash fears a California judge would nail him for child support.

Steve is on the stand right now ... and that's where he revealed he plans to stick around the NBA for a while. In fact, Steve said he has more than a year left on the lease for his sweet pad in Manhattan Beach, the city that a bunch of the Lakers call home.