Tartikoff’s Game Plan for Keeping NBC on Top : Ratings: The No. 1 network is fiddling with its powerhouse Thursday night lineup, adding “Grand,” a new sitcom.

Brandon Tartikoff, president of prime-time winner NBC Entertainment, held a closed-circuit press conference Monday. Among the announcements:

“Mancuso FBI” and “Sister Kate” have been picked up for the full season. The network had previously picked up “Baywatch,” “Hardball” and “Quantum Leap,” none of which appears so far to be headed for a niche in the Prime-time Pantheon.

Tartikoff also confirmed that his all-powerful Thursday night lineup is in for a change in mid-January, when a new sitcom called “Grand” replaces “Dear John” at 9:30.

“Dear John” will move to the 9:30 Wednesday time slot, replacing “My Two Dads,” which will repair to a new time slot, to be decided within the next couple of weeks. “Dear John,” meanwhile, has been renewed for the 1990-91 season, Tartikoff reported.

As described by NBC, “Grand” is “a semiserialized look at life in America this minute from three distinct socioeconomic viewpoints in the fictional town of Grand, Pa., a city struggling to regain its former glory.”

Tartikoff also predicted that negotiations with Bill Cosby for a seventh season of his high-rated series will conclude successfully very soon.

Tartikoff also revealed that the still mysterious one-hour drama series starring Alan Alda--the latter’s first TV series project in six years--starts production soon, that a pilot will be ready by May and that he’s hoping a spot can be found for it on the fall 1990 schedule.

Besides “Grand,” six other series are being considered as possible mid-season replacements: “Shannon’s Deal,” “Carol & Co.” (that’s Carol Burnett, playing a different character each week), “The Seinfeld Chronicle” (about a stand-up comic), “Down Home,” “Wings” and the radio station sitcom, “FM,” which has already had a tryout.