Fox Broadcasting Co. in January is planning to relaunch the summer reality series “Beyond Belief: Fact or Fiction” Fridays at 8 p.m. leading into “Millennium.”The series is replacing the now-canceled drama “The Visitor,” and it is expected to rejoin the Fox schedule Jan. 23, sources say. While “Beyond Belief” may not be the permanent resident in the timeslot, it will at least serve as a stopgap until the web can develop a compatible replacement. Over the summer and so far this season, reality shows have outperformed network expectations. Several one-time specials have been expanded into series, including CBS’ “Candid Camera” and “Kids Say the Darndest Things” and NBC’s “Bloopers.” Fox has also inked a few talent deals for projects that will be considered for slots in 1998. The web has signed a talent holding deal with Sue Costello, who has appeared on several episodes of “NYPD Blue” and starred in a CBS pilot. Fox also is developing a sitcom for comedian Dave Attell, who appeared with Drew Carey on HBO’s “Mr. Vegas All-Night Party” and HBO’s “1995 Young Comedians” special. The network has added some sup-porting cast members to its midseason comedy starring Vivica A. Fox, Duane Martin and Jon Cryer. Joining the cast is Elliott Gould, who starred in the features “Bob & Carol & Ted & Alice,” “MASH” and “Getting Straight,” among others. Also in supporting roles are Nancy Cassaro of “Temporarily Yours” and “Partners”; Reggie Hayes of “Nick Freno: Licensed Teacher”; and Selma Blair of “Soldier of Fortune.” The comedy is based in a Chicago production company and Gould plays the company CEO.