John Travolta just kicked even more ass in his legal war with the author of a book who claimed the actor frequented gay bathhouses ... and it's costing the author a bloody fortune.
You'll recall, Travolta was sued for libel by Robert Randolph -- the author of "You'll Never Spa in This Town Again" -- who claimed Travolta and his lawyer conspired to discredit him and his book by spreading lies about his mental health.
The court threw out the case back in September ... but now, adding salt to the wound, the judge has ordered the author to reimburse John for the entire legal bill ... to the tune of $139,645.17.
Travolta's attorney, legal pit bull Marty Singer, is fired up about the ruling ... telling TMZ, "This legal fee award is another complete and total victory for Mr. Travolta. Anyone else who files a ridiculous lawsuit against him should expect a similar outcome.”