Wayne agreed to plead GUILTY to a felony count of attempted criminal possession of a weapon in the second degree. In exchange, he accepted a one-year prison sentence.

He previously had pleaded not guilty to more serious charges of weapons possession and possession of a loaded weapon.

Back in 2007, New York police boarded Wayne's tour bus following a concert. The cops claimed they smelled pot . . . but in their search, they found a loaded .40-caliber pistol. Later, DNA evidence reportedly linked the gun to Lil Wayne.

Just so you know, the cops DID discover some weed on the bus . . . and arrested another unnamed man for possession of marijuana.

The trial was set to begin in January. If he'd been convicted of the original charges, he was looking at between three-and-a-half and 15 years in the clink.

He'll remain free on a previous bond of $30,000 . . . although he had to give up his passport.

Technically, Wayne won't be sentenced until February, but it sounds like the one-year sentence is definite . . . although with good behavior, it'll likely end up being something in the neighborhood of eight to 10 months.

Wayne has yet to issue a comment on the plea. As he was exiting the courthouse, reporters were asking him all kinds of questions . . . but his only response was, quote, "What's up?" (???)

All that being said . . . Lil Wayne is still not straight with the legal system. He's still facing felony drug possession and weapons charges from another tour bus raid. This one happened in Arizona last year.

Authorities there allegedly found 105 grams of marijuana . . . 29 grams of cocaine . . . 41 grams of ecstasy . . . various drug paraphernalia and a handgun.

Wayne has pleaded not guilty to the Arizona charges . . . and his trial in that case is scheduled to begin in March.