Matt, Meredith prepare for their chemistry test

“Today” co-anchor Matt Lauer was in the middle of describing a cellphone conversation with his newly hired on-air partner, Meredith Vieira, when -- in front of a roomful of reporters -- she interrupted to correct his account.

“Can I tell the story?” he retorted in mock exasperation. “Is this going to happen? I went through 10 years of this!”

“I thought you just screwed up again,” she said, patting his knee apologetically. “I was trying to help you.”

Sitting a few feet away and watching them teasingly spar at last week’s news conference, “Today’s” executive producer Jim Bell joked that he felt like crying. It was the first time he had gotten to see his new anchor team in action and the two were already needling each other like longtime friends.

“It was one thing to think it would work, but to actually see the two of them and how they played off each other -- it got me really jazzed to think about the possibilities of the show,” Bell said. “It’s hard to pin down why it happens or when it happens, but they just click together.”

Perhaps in no other type of news program is on-air chemistry as important as on morning television. “Today” built its decade-long winning streak largely on the repartee between Lauer and outgoing co-anchor Katie Couric, whose joking exchanges evolved over the years into the banter of a long-married couple. Once it became clear that Couric was seriously considering leaving the show to go to CBS News, finding another pairing that worked just as well became NBC’s top priority.

“That is the key ingredient,” said Phil Griffin, the news division’s senior vice president who oversees “Today.” “It is a very personal relationship in the morning, and I think you really make a connection with those hosts in the way you don’t with others on television. It’s critical that they be real and natural.”

So critical, in fact, that when ABC’s “Good Morning America” began closing in on the top-rated show last year, NBC executives decided it was largely because “Today’s” format had become too tightly scripted, giving Couric and Lauer little time to engage in spontaneous chatter. Bell was installed to reinvigorate it, and he immediately blocked out more time for unplanned riffs. Within months, “Today” had regained a wide lead.

Viewers seek anchors with an authentic camaraderie in the morning because it is an especially intimate time, said Stuart Fischoff, senior editor of the Journal of Media Psychology.

“It’s like getting married -- you’re inviting people into your home, your kitchen, even your bathroom,” he said. “The last thing you want are people who are going to annoy you.”

Although the elements of on-air chemistry are somewhat ineffable, it’s clear that much of it hinges on good-natured ribbing. When Bryant Gumbel and Jane Pauley started off as “Today” co-anchors in the early 1980s, producers understood the pairing would be successful once he began harping about how messy she kept her side of the desk and she, in turn, taunted him for being fastidious, Griffin noted.

“All of a sudden, these figures were human,” he said.

Less effective was Gumbel’s partnership with Deborah Norville, Pauley’s successor, whose formal demeanor did not mesh well with her co-anchor’s gruffness. She was quickly replaced by Couric, who took delight in teasing Gumbel when he became prickly. Soon afterward, “Today” regained its perch as the top-rated morning show.

Since then, its competitors have experimented with their own anchor combinations, trying to create an on-air dynamic that will help them challenge NBC. Over at “Good Morning America,” ABC bumped Robin Roberts up from the news desk to the anchor desk last year when executives saw that the former sportscaster added a folksiness to the interplay between Diane Sawyer and Charles Gibson. CBS -- whose five-person anchor team on “The Early Show” continues to lag far behind the competition -- recently recruited Steve Friedman, a veteran morning show producer, to reinvigorate the program.

When it came time for Lauer to consider a new partner, he said one of his top priorities was to find someone with a good sense of humor.

With Vieira, he was pleased to discover an immediate connection. The two had met briefly at various functions over the years, but they didn’t really get to know each other until this winter, when NBC officials began wooing “The View” co-host for the post in case Couric departed. During a phone conversation with her in December to set up a get-acquainted dinner at Lauer’s apartment, “there was a banter, an easiness in the conversation,” he said in an interview.

“It usually takes two people a little while to learn where the funny buttons are and testy buttons are, and it seemed we found that right away on the phone,” Lauer added.

“I think there was sort of an instant like, and you can’t fake that,” Vieira agreed in a separate interview. At that point, she was torn about whether she wanted to take on the grueling schedule required of an early-morning show. But the effortlessness of their interaction made her consider it more seriously.

“To me, it felt like a very good fit,” she said. “People want to feel comfortable with the folks that they’re watching. If you don’t have a comfort level, there’s something creepy about it.”

It remains to be seen how Lauer and Vieira’s dynamic will differ from the chemistry he and Couric have had. What resembled a “mock courtship” when Lauer joined the show in 1997 -- he was 39, she was 40 -- developed over the years into a more familial relationship.

“I’m going to miss Katie more than I think anyone knows,” said Lauer, now 48. “This is the one person who has sat by my side every single day, basically. We do know what each other is thinking and can complete each other’s sentences.”

On Friday morning, after introducing a piece about Vieira’s appointment as co-anchor, Lauer turned to Couric on-air and said apologetically, “I feel like I’m cheating on you.”

“It’s an amicable divorce, don’t you worry,” she replied with a grin, squeezing his hand.

With Couric, there has been “a playfulness with a longer history that started when we were younger broadcasters,” Lauer noted. He and 52-year-old Vieira are “coming together when we’re hopefully more mature emotionally and professionally, and maybe have a slight degree more seriousness in where we are.”

Still, both share a wry sense of humor and a tendency toward self-deprecation.

At one point during last week’s news conference, Vieira -- who has spent nearly a decade moderating “The View’s” all-female panel -- said she immediately took to Lauer and the three male NBC executives in charge of “Today,” suggesting that perhaps “because I’ve been nine years with four women that I’m just man-crazy. It’s become a lesbian or get a guy, I don’t know.”

Minutes later, her new co-anchor deadpanned: “I’m thrilled, Meredith, to know that it was me or a lesbian.”

Once she joins the program in September, Lauer said, it will be essential for them to let their relationship progress naturally.

“Where it goes from here, I don’t know,” he said. “The great thing about chemistry is as it develops, the audience gets to watch along with the people participating, and they feel they’ve grown with you. If we come on the air pretending we’ve developed this enormous chemistry, we take something from the process.”