By some fluke or mundane miracle, Dick Cavett does not interrupt his two-part interview with Ingrid Bergman to talk about his recent visit to Germany. From the way Cavett has rattled away about that particular excursion on his public TV talk show this season, you'd think the poor little tyke never got to take a trip before.

Cavett thought nothing of halting a compulsive raconteur like Robert Morley with another chapter in his gratuitous travelog, but it's obvious in the Bergman interview - tonight and tomorrow night at 11 on Channel 26 - that Cavett is still productively awestruck to be in Bergman's presence.

And so the encounter is warm and engrossing. Bergman may or may not be "one of the great ladies of the world" as Cavett claims her to be, but she certainly carries on like one - regal, lofty and lovable as a rich aunt.

Her new film, "Autumn Sonata," dutifully plugged by Cavett at the opening of each show, will be "my farewell to the movies," Bergman insists, and she tells about working with director Ingmar Bergman for the first time.

More fascinating is her recollection of hostile world reaction when in the late '40s she had Roberto Rossellini's baby, as they used to say, out of wedlock. Earlier, discussing her acting career, she says something that may apply to her generally: "I wanted to surprise people. I wanted to do something they didn't expect me to do."

In the second half, she reminisces briefly about making "Casablanca" and though she may have told these stories before, it is cheering to hear them again; any drop of juice about that picture being a true thirst-quencher for romantics of all ages.

"We never knew what we were doing from one day to another," she recalls of the hastily rewritten script, and remembers that her costar, Humphrey Bogart, "was angry all the time" because he thought the picture was being sloppily thrown together.

At one point Cavett apologizes for being too "probing," which is like Rod McKuen warning that his poetry might go over our heads. But Cavett clearly wants to avoid such interviewing pitifalls as the contentious confrontation approach of a Tom Snyder or the mania for melodrama of a Phil Donahue.

Though Cavett is far from perfect he never errs on the side of rudeness and now and again - as with Ingrid Bergman - he has the presence of mind and the sense of class to shut up. Good for him. I wonder if he has ever been to Germany.