For months, Fallon has been widely considered the top choice to succeed O'Brien when he steps down next year. On Thursday, published reports said Fallon has signed, or soon will sign, a deal with NBC.

NBC had no comment Thursday on the stories by The Hollywood Reporter and Variety. The network had been expected to announce its choice of host within the next few weeks, possibly at its May 12 presentation for advertisers.

A former regular on "Saturday Night Live," Fallon, 33, would take over sometime next year as host of the 12:30 a.m. talk show. O'Brien is to replace Jay Leno on NBC's "Tonight" show, aired at 11:30 p.m. each weeknight.

Fallon taking over "Late Night" is the only part of this talk-show turnover that remained in any doubt. The succession plan at the "Tonight" show, including Leno's departure, was announced by NBC in 2004.

But as long ago as last summer, NBC late-night boss Rick Ludwin was quoted as saying that Fallon "is at the top of our short list."