Chris Brown -- Stuck in Jail 'Til June ... At Least

Chris Brown will rot behind bars until June -- at the very least -- because the singer's latest bid for freedom was just DENIED.

Brown -- who was jailed last month after getting booted from rehab -- was flown to D.C. and promptly jailed as he awaited trial in his assault case.

The trial was supposed to start today ... but it was just postponed until June.

Brown asked the judge in the Rihanna beating case to release him, but the judge just shut him down.

Translation: Brown will soon be flown back to L.A. -- where he'll remain in jail until June ... at the very least. It looks like he'll be flown back to D.C. on Con air ... a trip way worse than economy.

The stakes are high ... if Brown is convicted in D.C. ... the judge in the Rihanna case could violate his probation and sentence Brown to four years in PRISON.