Channel 32 plans a half-hour special at 10:30 p.m. Tuesday covering highlights of the Congressional Black Caucus' 12th Annual Legislative Weekend that begins here today . . .

Here's a switch: NBC has given WNGE, the ABC affiliate in Nashville, rights to carry Johnny Carson's "Tonight Show," starting Oct. 4 . . .

How big a switch is it? It's so big that it's the first time ever, an NBC spokesman said yesterday, that Johnny's show will be on another network's affiliate . . .

The oddity arose after WSMV, the NBC affiliate in the 30th-largest market, told the network it was going to drop Carson on Sept. 27 because the network wouldn't let the station run Johnny on a delayed basis . . .

WSMV had been trying to get permission to slide Carson (who's been finishing third in his 10:30 time slot in Nashville) a half hour every night to 11 p.m., so the station's upcoming reruns of "Three's Company" could compete more successfully with WNGE's popular "M*A*S*H" reruns at 10:30 . . .

NBC has previously (and reluctantly) issued rare waivers to delay Carson for affiliates in Minneapolis, Milwaukee and Birmingham as "an experiment," but sensing that an "experiment" can quickly mushroom into a network-wide trend, NBC said "no way" to WSMV . . .

Oddly, the eagerness with which Carson was snapped up by the ABC rival now has NBC executives feeling pretty good about its new strategy . . .

Shakeup in the higher echelons of ABC, where ABC Television president John Severino has taken over the ABC owned-stations division . . . resulting in yesterday's announcement that Richard O'Leary, the former O-&-O boss, will be leaving at the end of the year to form his own company . . . whose best customer, in the manner in which these things are always handled at the networks, will be ABC . . .

One week does not a turnaround make, as Captain Airwaves must constantly remind Certain Executive Producers, but NBC's "Today" . . . with a little help from Lana Turner . . . did achieve its highest ratings last week since the week ending May 3 and its biggest audience share since January . . . and even came close to "Good Morning America" . . .

Still stung by a recent article in Newsweek suggesting "Today" may have run out of steam altogether . . . the network called yesterday to report that for the week ending Sept. 10, the NBC show had a 4.6 Nielsen and a 26 audience share, compared with GMA's 4.9/28 and "CBS Morning News'" 2.4/14 (the lowest that program has been since February) . . .

NBC's "Early Today" also edged a little closer to ABC News' "This Morning" in the early-early race last week . . . but together they still are barely attracting 2.6 percent of the potential TV audience from 6 to 7 a.m. . . .

Officials of WNET in New York would like to open negotiations with CBS Cable over the rights to its "A Walk Through the 20th Century With Bill Moyers" series as well as the system's interview program, "Signature". . .

CBS Inc. announced earlier this week it is folding the cultural cable TV system within 90 days for lack of advertising support . . .

However, a CBS Cable executive told us yesterday there's little chance for the Moyers series to move to PBS, if for no other reason than CBS News would like to keep him identified with CBS . . .

"We have several options," the executive told us, "including airing those programs on the CBS network, and no decisions have been made yet" . . .

He said work has been completed on all 21 shows in the "Walk Through the 20th Century" series short of wraparounds and that "between seven or eight of the programs -- at the rate of two a month -- will air through December on CBS Cable" before the system closes down . . .

ABC Sports says that the 13th season opener for its Monday Night Football twixt Pittsburgh and Dallas set an opening game ratings record, attracting 32 million viewers with its 24.9 Nielsen rating and 42 percent audience share . . .

Previous opening-night record holder: the Redskins-Cowboys game on Sept. 8, 1980, with a 23.4/40 . . .

Johnny Holliday is co-host of "In the Locker Room," with Maryland football coach Bob Ross, that airs on Channel 20 at 11:30 Sunday nights and 11 p.m. Sundays on Channel 45 . . .