President Reagan didn't show up on "The Tonight Show" Wednesday after his Mideast speech at the NBC Burbank studios, after all . . .

He didn't finish his address until 6:20 p.m. (PDT) and by the time he had paused for a photo opportunity and shaken hands with the TV crew, the Secret Service was moving him out to the NBC heliport and the trip back to the ranch . . . just as Johnny Carson was finishing his taping down the hall at 6:30 . . .

NBC executives were aware, too, that the serious nature of the president's address ruled out a jaunty appearance on "Tonight" . . .

The "Today" show made one of its rare passes at the early morning network leadership last week, but "Good Morning America," even without David Hartman, prevailed . . . and for the 30th week in a row. . .

Nielsen ratings for the week ending August 27 show GMA with a 4.5 rating and an average audience share of 26 percent, compared with "Today's" 4.2/24 and "CBS Morning News' " 2.8/16 . . .

The "Today" show also announced yesterday it will introduce a new celebrity interview series, to be called "Close Encounters," sometime in October that will feature two celebrities interviewing each other! . . .

Executive producer Steve Friedman said the idea was first suggested two years ago by Joan Kennedy. . .

Friedman said that Kennedy is a possible guest in the new format and that he hopes to have film producer Steven Spielberg interview an astronaut . . .

The segments could run 6 to 7 minutes . . . as "Today" also plans to lengthen its features when the new season gets under way. . .

NBC president Robert Mulholland is heading a contingent of 14 . . . including two vice presidents from parent RCA . . . currently visiting Seoul, Korea, as that network makes a pitch for the 1988 Summer Olympics . . .

Also in the NBC party is consultant Richard Holbrooke . . .

The former assistant secretary of state for East Asian and Pacific affairs during the Carter administration now heads Public Strategy here . . .

All three networks are making vigorous cases for the 1988 Games, which could cost double the $225 million paid by ABC for the 1984 Games in Los Angeles. . .

A CBS Sports executive visited Seoul two weeks ago and ABC Inc. president Elton Rule visited the Korean capital earlier this summer . . .

The presence of the RCA executives in the NBC party suggests to the rival networks that NBC is prepared to sweeten its package with satellite services and even a rental car deal (RCA includes Hertz) as it makes its case to Korean Olympic officials . . .

Serious negotiations begin next year.