EXCLUSIVE

It's an enormous sea change ... one of the most successful shows in the history of TV -- a show that has made BILLIONS of dollars in profits -- will actually LOSE money this year ... multiple sources connected with the show tell TMZ.

The reasons for "American Idol" going into the red for the first time all have to do with the bottom line. The show pays a fortune to the stars -- we're told Jennifer Lopez gets north of $15 Mil and Ryan Seacrest gets around that amount as well. They spent between $5 and $7 million on a new set this year. They are also still paying the 2 executive producers they fired after last season.

In addition we're told the show will spend at least $5 million on viewer phone calls.

And ... the ratings are down 26% from last season -- and that translates into advertising dollars. Some of the ad losses can be deferred until next season ... but they are losses nonetheless.

For years "Idol" scored hundreds of millions of dollars in raw profits in a single season.

That said ... we're told the show almost certainly will NOT be cancelled after this season. Sources say it will be back next year, in no small part because FOX cancelled "X Factor" and there would be way too many holes in its primetime schedule if both shows went away.

Now perspective ... "American Idol" is one of the most successful shows ever on television. Almost no shows make it to season 13 and the ratings for the show's run have been unbelievable.