Justin Bieber -- Pound Sand DUI Prosecutor ... I REJECT Your Plea Deal

Justin Bieber will REJECT the plea deal prosecutors in his Miami Beach DUI case have offered ... and a big reason is because he doesn't want random drug testing.

TMZ broke the story ... prosecutors offered Bieber a deal they often give to first-time DUI offenders ... it includes community service, an alcohol ed course and random drug testing.

Sources connected to Bieber tell TMZ ... there are several reasons they aren't buying what prosecutors are selling. First, there are huge problems with the case -- they believe the cop lied when he said Bieber reeked of booze (he only blew a .014), and he was also lying about observing Bieber drag race -- the GPS device registered a very reasonable 27 MPH.

But the bigger issue is this -- our sources say Bieber will NOT accept any plea that has probation ... where the judge can throw the book at him if he screws up.

In particular there's NO WAY Bieber will agree to random drug testing. Fact is ... he has a problem with weed and sizzurp. If you don't understand his worry, just remember Lindsay Lohan, who became a habitual probation offender for more than 7 years.

Also, we're told Justin will not accept an alcohol ed course as part of a plea deal, because he'd become a spectacle.

We're told Bieber is open to a plea ... but not this one.