By GARY LEVIN

NBC on Monday officially named Matt Lauer to replace Bryant Gumbel as co-anchor of "Today," the leading ayem network talkshow.

The move, widely expected for months, puts Lauer, 38, in "Today's" newsreader slot Jan. 6, slipping into Gumbel's chair alongside Katie Couric. That follows a two-hour Gumbel tribute sendoff honoring his 15 years at the "Today" anchor desk.

Although NBC News president Andrew Lack said he considered other candidates, Lauer led the field, and the anchor himself said he "assumed I had a good chance because I was the only one who filled in for Bryant."

Eye on 'America'

Lauer said he's "very comfortable" handling both news and celebrity interviews, the twin staples of the format, but allowed that "the most difficult part of the job is quick changes of gears between subject matter," a skill at which Gumbel excels, he said. But Lauer said the inevitable comparisons with Gumbel, who has helped nurture the chatfest and eclipsed ABC's "Good Morning America," will prove "the biggest hurdle for me."

"I hope people don't turn me on on the sixth and expect to see me do my imitation of Bryant," he said. "That would be wrong."

Familiar face

And Lack believes "Today's" ratings won't suffer from Gumbel's absence, even temporarily, because the web hasn't "parachuted someone in who has not (already) been connected to the show." Lack said no other format changes are planned, except that behind the scenes Lauer and Couric have been designated equal co-anchors, a status Couric didn't have alongside Gumbel. Terms of Lauer's multiyear contract weren't disclosed, nor has his permanent replacement as news anchor been named.

Lauer, at "Today" for the past two years, also anchored WNBC New York's "Today in New York" and "Live at Five," partly overlapping his network stint. Before joining WNBC in 1992, he anchored a live morning talkshow at WWOR New York.

As for Gumbel, who's entertaining offers from CBS and ABC, Lack insisted that NBC still is eager to keep him, but declined to discuss specific proposals. It's clear however, that NBC's rivals have dangled more tantalizing opportunities before Gumbel, as he's less likely to find major roles immediately in the offing at the Peacock's "Dateline NBC" or other news programs. And most news execs expect Gumbel to bolt in early '97.