In the wake of the news that Roger Colloff has been named vice president for division services for the CBS Television Station division . . . there is considerable speculation at CBS News about who gets Colloff's old job as vice president, director of public affairs broadcasts . . .

Among the top candidates is George Schweitzer, who was CBS News president Van Gordon Sauter's right hand when the latter ran CBS Sports, but returned to a top post at CBS/Broadcast Group when Sauter moved to News . . .

Colloff, a former aide to vice president Walter Mondale, has been considered one of the rising young executives at the network despite a comparatively short term in the TV news business . . .

He was one of the key CBS News veeps who signed off on the controversial Vietnam documentary that is now the subject of a $120 million lawsuit brought against CBS by Gen. William Westmoreland . . .

Colloff's new assignment reportedly puts him in line for a job as a station manager at one of the network's five owned outlets . . . in New York, Chicago, Los Angeles, St. Louis or Philadelphia . . .

In theory, that puts him on the fast management track that usually leads to CBS News headquarters in New York . . . to a job like vice president, director of public affairs broadcasts, which, under Colloff, included oversight of "60 Minutes" as well as CBS Reports and other public affairs specials . . .

David Cohen, formerly a news producer at WPLG in Miami, began work as producer for Channel 5's 10 o'clock news yesterday . . .

He replaces Densil Allen . . .

Catherine Zimmerman, who has been a news photographer at Channel 7 since 1978, has joined the station's new Creative Services (i.e., documentary) Unit as a photographer-editor . . .

R. Peter Porello, who has been director, personnel and labor relations, for NBC in Washington since 1981 . . . has been named vice president, personnel, NBC in New York, which makes him responsible for all personnel functions within NBC . . .

Although we're comparing this year's two-hour version against last year's 90-minute version . . . "CBS Morning News" is showing a 29 percent increase in audience so far this fall season over the same period last year . . .

CBS has averaged a 3.1 Nielsen rating and a 16 percent audience share so far this fall, compared to a 2.4/13 in 1981 . . .

Likewise, ABC's "Good Morning America" with a 5.5/28 (up from a 5.l/28) is up 8 percent over last year from the week ending Oct. 10 through Nov. 26 . . . while NBC's "Today" at 4.3/22 (down from 4.8/26) is off 10 percent from the same period last year . . .

Baltimore was one of only three TV markets (along with St. Louis and Minneapolis-St. Paul) in which NBC ran over with its second NFL game Sunday night . . . and that's why, since the great majority of the network stations were on schedule for regular prime-time programming at 7, viewers in those markets joined the Bataan special in progress . . .