Mrs. Brady, TV's Uebermom, is joining NBC News.

Florence Henderson, known to millions as Carol Brady in "The Brady Bunch," has been signed to co-host "Later Today," which debuts Sept. 7, following the "Today" show.

Henderson played a widow with three daughters who married an architect with three sons on the popular sitcom, which ran on ABC from 1969 to 1974 and became a camp classic and the subject of two 1990s hit movie spoofs. (She also reprised the role in two short-lived series in 1977 and 1990.)

But how, you might ask, did the 65-year-old cult figure segue into a co-host gig on an NBC News program?

Here's the story of a lovely lady, who was bringing out her very lovely new cookbook on the morning-show circuit last September. Then one day, she was seen on "Today" by Jeff Zucker, and he knew it was much more than a hunch that Mrs. Brady must somehow join his family, and that's the way she became part of the "Later Today" bunch.

This hire is so weird that when a brief item about it ran a month ago in the trade paper Variety, nobody believed it.

Actually, it makes a lot of sense, once the initial shock wears off. Before there was the "Today" show's Barbara Walters, there was "Today's" Florence Henderson. She was a " 'Today' Girl" in 1959, when Dave Garroway was the program's host, and concepts like " 'Today' Girls" were politically acceptable. Henderson contributed interviews and features to the broadcast.

Beyond that, she's what the TV business calls pre-sold--beloved by 33 percent of the nation's households who religiously watched "The Brady Bunch" at its peak in 1971 and millions more who caught it in reruns, not to mention her GenX&Y draw thanks to Nick at Nite. She also has "a certain Wessonality" from her 21 years as a TV spokeswoman for Wesson Oil. Then there's the whole Tang Mom thing.

Well, station executives are buying into the idea, anyway. NBC stations covering 70 percent of the country's TV audience have already agreed to carry the show in its designated 9 a.m. time slot, though no format has been developed yet. The show it's replacing, "Leeza," has dropped below 50 percent coverage in its time period.

Meanwhile, MSNBC "Morning Blend" anchor Soledad O'Brien has been tapped to take over for Jodi Applegate as host of the weekend edition of NBC News's "Today" show when Applegate joins Henderson on "Later Today."

O'Brien, who has been a substitute anchor for the weekend "Today," is to assume her new post in August, sources say. NBC's not talking. In addition to anchoring MSNBC's three-hour weekend talk show "Morning Blend," O'Brien reports for "Nightly News" and "Dateline" and has substitute-anchored weekend "Nightly News." Before taking on "Morning Blend," she caught the attention of NBC News brass as host of MSNBC's "The Site" show about new technology.

Look for Jerry Seinfeld to open the 1999-2000 season of NBC's "Saturday Night Live." The network wants Seinfeld to kick off the late-night comedy show's 25th anniversary. One source says there's an offer out to the stand-up-turned-sitcom-star- turned-multimillionaire. Another describes it as an all-but-done deal.

The question is, would Seinfeld be able to outdraw Ricky Martin and Monica Lewinsky? Last season's most watched "SNL," featuring the singing sensation, the former Clinton gal pal and host Cuba Gooding Jr., drew 10.7 million viewers. That beat the following Saturday's "SNL" season finale, which featured Buffy the vampire slayer, a k a Sarah Michelle Gellar, and the Backstreet Boys and drew an audience of 8.3 million.

On the other hand, Seinfeld's prime-time series so-long, which aired a year earlier, sucked in a whopping 76 million fans.

CNBC anchor Chris Matthews may be moving to MSNBC and making seven figures in the not-too-distant future.

Matthews is close to a new long-term deal with CNBC and MSNBC parent NBC, though nothing is signed yet, says a source close to the negotiations.

If Wall Street expands its trading hours as planned, CNBC may expand its business coverage, in which case "Hardball" is a likely candidate to move to sister cable network MSNBC. Or, the talk show may run on both networks, one source said. "The key is flexibility . . . the new deal would allow the network flexibility, which is important in this changing situation," the source added.

In return, Matthews's salary, currently cited as $500,000 a year in press reports, would shoot up to seven figures, the source says.

Matthews, Washington bureau chief for the San Francisco Examiner, has been with CNBC since 1995. In this quarter to date, "Hardball" is averaging 438,000 households, down from the same period last year (484,000 households). "Hardball's" lead-out, "Rivera Live," is averaging 490,000 households this quarter, down from 646,000 homes in the same period last year, according to Nielsen numbers.

A CNBC representative declined to comment on the report.

CAPTION: Florence Henderson, center left, co-star of the '70s sitcom classic "The Brady Bunch," will co-anchor "Later Today" on NBC this fall, when Jerry Seinfeld, above, may host "Saturday Night Live's" season opener.