At WCBS-TV, a Big Round Of News Staff Dismissals

WCBS-TV/Channel 2, a perennial third place in the local news ratings race, yesterday dismissed some of its best-known on-air journalists, including anchor persons John Johnson, Michele Marsh and Tony Guida, sportscaster Bernie Smilovitz and reporters Magee Hickey, Roseanne Colletti and Reggie Harris.

WCBS, along with most of the other local stations owned by CBS, a unit of the Westinghouse Electric Corporation, has long underperformed stations owned by other networks. And local news broadcasts are by far the biggest money makers for such stations.

Westinghouse quickly signaled its interest in local stations when it bought CBS last year by replacing the CBS executive in charge of the stations with Jonathan Klein, a former Westinghouse executive.

''This station has been underperforming in news programs for 20 years,'' said Carl (Bud) Carey, the vice president and general manager of the station, who started issuing the dismissals at about 5 P.M. last night.

''Rather than go through the charade of piecemeal change here and there, we want to recruit new people to build something a little different,'' he said.

The firings were effective immediately, Mr. Carey said.

Turmoil at the station began last month, when Jerry Nachman was dismissed as news director after two years. Mr. Nachman had tried to invigorate the news programs with local news talent, hiring Mr. Johnson away from WABC-TV/Channel 7, and Ms. Hickey, from WNBC-TV/ Channel 4.

More dismissals had been expected in the wake of Mr. Nachman's departure.

Mr. Carey said the ratings problem at the station went beyond lacking popular lead-ins to the 5 P.M. and 6 P.M. news, like Channel 7's ''Oprah,'' or a 10 P.M. powerhouse like ''E.R.,'' which precedes Channel 4's 11 P.M. news show.

''Even on Monday nights, when we have a good lead-in with 'Chicago Hope,' our ratings fall off sharply from that,'' Mr. Carey said. ''I judge people for what they tune to. And they tune to Channel 7.''

On Tuesday night, Channel 2's 11 P.M. newscast posted a 6.3 Nielsen rating, trailing the 9.7 for Channel 7 and the 8.2 for Channel 4. At 6 P.M. the gap is even wider: Channel 2 had a 2.4 rating, Channel 7 a 6.9 and Channel 4 a 5.9.

Temporary changes made by the station include: Dana Tyler and Lou Young will replace Mr. Johnson and Ms. Marsh on the 5 P.M. newscast; Vince DeMentri will succeed Mr. Guida and Ms. Tyler at 6 P.M., and Ms. Tyler will take over for Ms. Johnson and Ms. Marsh at 11 P.M.

Ira Joe Fisher remains as the weather forecaster and Dave Sims, who is now the weekend sportscaster, will take over for Mr. Smilovitz.