Dr. Conrad Murray took a $16,000 hit today -- when officials rejected his request to relieve the massive child support debt he owes his baby mama.

Murray -- who practices medicine in Nevada -- had worked out a deal with Nevada State Board of Medical Examiners, in which they'd back off from revoking his license ... if he could convince a California court to forgive the $16,000 in back child support he owes in Cali.

But today, a judge in California turned down the request -- which means Murray's license is still very much in danger.

And check this out -- a hearing was scheduled to be in Nevada for June 25th ... exactly one साल after Murray allegedly pumped Michael Jackson full of a deadly dose of Propofol.