Ruth Slawson is leaving her post as senior VP of movies and miniseries at NBC , marking the firstmajor exec change since Don Ohlmeyer took over as president of the network’s West Coast operations last month.Lindy DeKoven, Lorimar TV’s VP of movies and miniseries, is expected to replace Slawson, though the deal reportedly is still being negotiated. DeKoven joined Lorimar two years ago and has spurred an increase in telefilm activity at the Time Warner unit, TV’s leading supplier of prime time series. Before that she served as VP, creative affairs, at the Landsburg Co., worked as director of network development at Walt Disney TV and headed her own company, Carter-DeKoven Prods. Producer Karen Danaher-Dorr has also been mentioned as an outside candidate for an NBC post. Danaher-Dorr is at Republic Pictures under an exclusive production deal, inked in January 1991, that was preceded by a similar pact at Ohlmeyer Communications Co., the new NBC chief’s firm. NBC confirmed Slawson’s exit late yesterday but wouldn’t discuss a successor. In a statement, NBC Entertainment president Warren Littlefield called her “an important contributor to NBC.” Structurally, Slawson reported to exec VP of prime time programs Perry Simon. An eight-year NBC veteran, Slawson became head of the longform department in January 1991 after Tony Masucci left to pursue independent production. She started at the Peacock web as director of movies for TV, becoming VP of miniseries in February 1989 and overseeing such ratings successes as “Blind Faith,”"Jackie Collins’ Lucky/Chances” and “I Know My First Name Is Steven.” Still, the network, which has slid into third place this season, has also taken a hit in its longform results. A clear blow — and to some observers the final straw — came during the February sweeps when the miniseries “Bloodlines: Murder in the Family” averaged a 12 rating/19 share over two nights — the worst results for a regular-season multiparter since ABC’s “Separate but Equal” in April 1991. Ironically, “Bloodlines” is from DeKoven’s current home, Lorimar. In Slawson’s defense, one source maintained recent movie troubles can in part be attributed to the general malaise at the network. “It’s just that nobody’s watching NBC, so nobody’s even seeing the promos for their movies,” he said. The web’s highest-rated vidpic this season was its get-there-first Amy Fisher entry, “Amy Fisher: My Story” (19.1/30). Perhaps the most prestigious accomplishment during Slawson’s tenure came during last year’s Emmy Awards, when NBC took honors for both outstanding movie and miniseries: the Hallmark Hall of Fame “Miss Rose White” and the six-hour production “A Woman Named Jackie.” Observers add Slawson’s mandate was to appeal to the age 18-49 demographic — the key group in terms of sales — and that NBC presented four of the top six movies by that standard in February. Ohlmeyer, who has talked about the web’s need to broaden its appeal since taking over, is said to have been active lately in dealings for TV movies, spearheading efforts to turn around telefilms based on the World Trade Center bombing and the standoff involving cult leader David Koresh in time for the just-around-the-corner May sweeps (Daily Variety, March 5). Those projects are from Wilshire Court Prods. and Patchett Kaufman Entertainment, respectively.