Nancy Dickerson is smiling, but the smile is tight and forced. Actually, Nancy Dickerson is very ticked off, very ticked off indeed.

She gets up from her desk, a willowy, well-tended auburn-haired lady in her mid-fifties, looking very chic in a black-and-white checked Bill Blass suit. She paces the floor, then rather pointedly closes the door of her office, lest her executive assistant or assistant producer, working down the hall, overhear what she is about to say.

Why is Nancy Dickerson ticked off? Well, she reminds, the reason she had agreed, finally, to do this interview was to publicize her documentary.

She is sitting in the tastefully appointed, antique-laden Georgetown town-house office of Television Corporation of America, Dickerson's recently formed television company, the company that is producing "784 Days That Changed America: From Watergate to Resignation," a two-hour documentary, 10 years after the break-in, to be aired this Thursday at 8 on Channel 5.

This is what she agreed to talk about, she reiterates. She feels deceived, she says, and strongly suggests the reporter may have misrepresented himself. "I've refused numerous requests for interviews, because I don't want to talk about my personal life," she declares.

"All these people you've been talking to," she goes on, "my friends, my ex-husband, people I worked with at NBC, asking them if this show is a comeback for me, asking me if my emeralds are real . . ."

The reporter says he doesn't recall asking such a question during the previous interview, several weeks earlier.

"You did! You did!" she insists, her face fairly contorted with rage. "You definitely did! I remember it!"

The reporter remembers the emeralds. Who wouldn't remember the emeralds? It was 3 o'clock in the afternoon, but Dickerson could have passed muster at Buckingham Palace--emerald pin, emerald bracelet, gold-and-emerald necklace and two large emerald rings.

There was a time, back in the '60s, when Nancy Dickerson would have needed no introduction at all. She was practically a Washington household word--at least in some households--a ubiquitous presence, a confidant of JFK and LBJ and other Washington power figures, a "sexy madonna," in the words of one of her mentors, Edward R. Murrow, and a pioneering woman, first at CBS, then at NBC, in the fiercely competitive, rough-and-tumble world of network television news.

Then, late in 1970, Nancy Dickerson suddenly left NBC, for reasons about which there is still occasional speculation in media circles, and after a brief, frustrating bout with free-lance syndication, seemed to do a slow fade--professionally, at least.

Socially, it was something else again. Married in 1962 to entrepreneur-developer-consultant Wyatt Dickerson, she became the mistress of Merrywood, a showplace mansion high above the Potomac in McLean, Va., the girlhood home of Jacqueline Bouvier Kennedy Onassis. It was a time of high visibility--climaxed, probably, by the glittery dinner given in January 1981 for President-elect and Mrs. Reagan's close California friends, the Armand Deutsches. Of course the Reagans attended, and so did Frank and Barbara Sinatra, among other Reagan supporters.

Now Dickerson's 20-year marriage is over. "I'm separated--legally separated, divorce pending," she replies tersely to a question. Merrywood is up for sale (asking price: $5 million). Wyatt Dickerson has taken up with blond Washington socialite Tandy Dickinson, former companion of Tongsun Park, Wyatt Dickerson's former business partner in Pisces, the posh private club in Georgetown. Nancy Dickerson has been seeing Texas oilman Bill Moss, formerly married to movie stars Ann Miller and Jane Withers. Moss is said to be the major bankroller for Nancy Dickerson's television company. This she won't confirm or deny. "It's a privately held company," she says of TCA. "There are several partners."

On the Watergate documentary, Dickerson is much more informative.

I've been working day and night on this," she says. "I have watched 167 hours of tapes, Watergate news conferences, nightly news programs--the most TV I have seen in my life.

"It's been a regular treasure hunt," she goes on. "We are compressing two years into two hours."

And while Nancy Dickerson is writer, narrator and executive producer for the show, she hastens to add that "I'm not doing it all myself." She has assembled a team of "seasoned professionals" to help put it together--including co-executive producer Bill Carpenter, former general manager at WTTG-Channel 5, whose idea the show was, and cinema ve'rite' documentary specialist Bob Drew of Bob Drew Associates in New York, where the show was being assembled. Barry Sussman, city editor of The Washington Post at the time of Watergate, was a consultant, Dickerson says, and they used his book, "The Great Cover-Up," as a guide.

"We've had 15 people working on it--10 people full time since last December," she says. "We've had people at the library at Vanderbilt University, where all the taped material is stored, people at the archives . . . about 300 hours of tape exist, you know . . .

"I will tell you, something like this is an extraordinary effort, and it's a very sobering experience going through all this material again--the whole period--it's such a nightmare . . . Nixon is such a tragic figure . . ."

Watergate Revisited

She also conducted interviews with Judge John Sirica, John Ehrlichman, Elliot Richardson and Gerald Ford. She tried for Richard Nixon--"four, no, five times," she says--but didn't get him.

Most of the roughly 60 stations that bought the program--independents and network affiliates--are running the show on Thursday, June 17, the 10th anniversary of the break-in. "Channel 5 is carrying it here," she says, "and we're pretty much all over the country--70 percent of the country.

"None of the networks had the gumption to do this, to take this long a retrospective look," she goes on. "The 'Today' Show is interviewing Judge Sirica. ABC is doing something, but not like we're doing. We want to show it like it was. I really believe it will have an impact. We're not spoon-feeding--it will not put you to sleep, I assure you . . ."

So what's this long retrospective look costing TCA? She hesitates, then gets Bill Carpenter, who's also syndicating the show, on the intercom. "Bill, can we say how much this show is costing us?" She laughs. "Bill says no, it can only come back to haunt us."

Dickerson wants, however, to quash the notion that this show is any sort of television "comeback" for her. She's offended by the term. In her own mind, despite the irregularity of her appearances in recent years, she has never been away.

"I've done a number of things for PBS," she says. "I did a special about single-issue politics, 'A House Divided,' and one on the energy crisis, 'We Will Freeze in the Dark,' and another one about women in the Arab world, 'Islam: The Veil and the Future' . . . . About a year ago I did a Middle East special, I interviewed Prime Minister Begin . . . Sadat and the foreign minister of Saudi Arabia, Prince Saud, the first time the three of them were together on one program . . . Sadat was so sensual and attractive," she recalls. "He really had dark skin. His mother was from Uganda. You might call him . . . black."

She also interviewed President Reagan, Vice President Bush and top White House officials last year for an International Communication Agency film, "The Reagan White House," she points out.

Still, continuity of image is important in television, and when you mention Nancy Dickerson to someone 25 or 30 years old, even a Washington news reporter, you can draw a blank, she is told. It doesn't seem to concern her. "They know me around the country," she says.

The Women of TV News

But isn't this a kind of comedown for the self-styled "first lady" of network television news--being relegated to women's club lectures and an occasional special on PBS? Shouldn't Dickerson be more prominent today? Shouldn't she be up there with Barbara Walters?

There is a long, thoughtful pause at the mention of Walters. Dickerson looks pensive, speaks very carefully. "Barbara is having . . . a wonderful career," she says, slowly. "I think some of the interviews she's done have been marvelous. Of course, some of the shows she's done are celebrity interviews . . . movie stars . . ." That wouldn't be Dickerson's approach, it's suggested. "No," she says firmly. "I have an entirely different approach."

Dickerson's approach has always been more news-oriented, but there are those in the news business, especially other women, who think that despite her style and telegenic looks, she's a lightweight, that she got where she was by charming influential and powerful men like Sen. Kenneth Keating (an early benefactor and serious romance), Henry Jackson, Jack Kennedy and Lyndon Johnson--especially Lyndon Johnson, whose "Hello, Nancy," became her TV trademark. Some thought that they were having an affair. Dickerson denies it. LBJ propositioned her "only once," she maintained in her 1976 autobiography, "Among Those Present," but aide Bill Moyers helped her deflect LBJ's advances on that occasion, she wrote. "To tell the truth, I didn't find LBJ very sexy," Dickerson wrote.

She was, nevertheless, a pioneering woman in TV news--a bright, attractive, ambitious Catholic girl from Wauwatosa, Wis., "where nothing ever happened," with a keen interest in world affairs and world leaders, who went from a staff job on the Senate Foreign Relations Committee to a major television career. Major for a while, at least.

"I'm proud of it," she says. "There were a lot of firsts. I was the first woman to do a daily network news show, the first woman on the floor of a convention, the first woman in an anchor booth, the first woman to broadcast from the floor of the Senate . . ." Leaving NBC -------------

"She did a very, very good job for us," says Frank Jordan, then NBC Washington bureau chief, now professor of communications at American University. "She's a good reporter, she worked at it, she had a lot of contacts, she knew instinctively how to work the city. I really do give her all kinds of high marks. She would come in with good stories, really dig up good stories. She was, as I recall, not assigned to a beat, not assigned to the Senate, the House, or White House, which gave her a flexibility . . ."

"She was a hard worker, and a perfectionist," says NBC producer Bob Asman. "I remember once when Nancy did at least eight takes in a pouring rain, the script literally turning to pulp in her hands, but she wanted to get it right. That was typical of her. But she had to take a lot of slings and arrows. People were very envious and resentful of her access to LBJ, for one thing."

She wasn't very well-liked. Too aloof, many said; too impressed with herself, too much the prima donna, the social climber, too hard on her coworkers (staff turnover in her office, former colleagues say, was high, both at CBS and NBC); too prone to flaunt her jewelry, her designer dresses, her mink coat when working a beat with other, less affluent reporters.

So when Dickerson left NBC late in 1970, people who knew her suspected all sorts of things, mainly the worst--that she was getting too big for her britches; that too many people hated her at NBC; that her social pretensions compromised her credibility as a serious reporter; that her husband, who always took a very active interest in her career, tried to drive too hard a contract bargain with the network.

Wyatt Dickerson denies it. "I was not involved in the negotiations for her last contract," he says. "I was involved in earlier ones. Anyway, Nancy was never that concerned about the money. It was the job that mattered to her, what the job entailed. And they weren't really utilizing her at that point."

Nancy Dickerson more or less agrees with that analysis. In her autobiography she expressed dissatisfaction with the assignments NBC was giving her, starting with the 1968 conventions, when she "suffered the backlash of women's lib, finding myself relegated to secondary stories, secondary position."

"I'm not certain in my own mind why she left," says Frank Jordan. "She resigned. There was nothing that untoward about it. She had done everything that she could do at NBC News, and that involved breaking down a lot of barriers. People leave. It happens with some frequency. I liked her and respected her. She was an asset, there is no doubt about it. I'm sorry that she left. On the other hand, I think it was a case of what she wanted to do at that point, and what NBC could make room for her to do, didn't jibe."

Yes, Jordan acknowledges, "there was some hostility to her, talking behind her back, denigrating, that is true. I can't recall Nancy Dickerson ever complaining to me about anybody else. Nancy Dickerson would never come in to tell me denigrating stories about her colleagues . . . This aloofness you mention--could it be that she was just shy?

"Women in television today owe her a lot," Jordan goes on. "They don't know what it was like back there. Women who now find it easy to criticize Nancy Dickerson don't realize, some of them are where they are today because of Nancy Dickerson. I really mean that."

No Regrets

The reason Dickerson gives for not wanting to discuss her personal life, particularly the impending divorce, is because the children are involved. (Michael, 19, will be a sophomore at Stanford next year, and John, 14, goes to Sidwell Friends School.) She is concerned about the children. "You remember how you were at that age . . . so sensitive about things, items in gossip columns . . ." Do they read? "Of course they read!" she snaps.

Even Nancy Dickerson's detractors give her credit for being a devoted mother. Her close friends say she is truly pained by the prospect of divorce. They also say that if there's a villain in this piece, it has to be Wyatt Dickerson. Wyatt Dickerson, much like a shrewd Hollywood promoter, they say, latched on to a famous name, a viable property, and used her connections to gain Washington entre'e, social acceptability and access. The publicity about his business deals, they say, had a negative effect on Nancy Dickerson's television career, not to mention her social standing.

Wyatt Dickerson doesn't see it that way, of course. "She wasn't a famous name when I married her," he says. But he doesn't want to discuss "anything personal" either.

Looking back, does Dickerson feel any regret today for the network career that might have been? "I don't say it bothers me," she says. "Oh, I suppose if I'd gotten a million dollars, life would be sweet and easy . . . You know, along the way, I did raise five children (including three step-daughters, now grown, by Wyatt's previous marriage). I haven't been just sitting around."

If NBC had made her an anchorwoman, would she have stayed? She smiles. "I anchored a show for six years, four times a day, the five-minute news shows. They called them strip shows. It isn't hard work, you know. What you do, you rip the wire, you rewrite the wire, you read the wire. The most exciting thing in television is being on a story live--election night, or a convention, any of those things that you do live . . . but they take a lot of ability . . .

"I suppose one would like to be on regularly," she admits. "It's been a very sometime thing, and it isn't always easy, having to write and produce it, and having to deal with a pickup crew in a foreign country in hundred-degree heat. Being with a network, that's a very helpful umbrella."

Of course, she is committed now to her own independent company, TCA. "This is our first major production, and we want to keep the momentum," she says. "Of course Bill and I have plans to do other shows--public service shows," she emphasizes. "It won't be any 'I Love Lucy.' "

But now she really can't talk any more, she says. She's running late. She's over at the mirror, combing her hair, then sitting at her desk again, applying a darker shade of lipstick. Someone has just phoned, someone she doesn't identify, naturally, but she suggests they meet shortly at Pisces, a few blocks away. She plans a two- or three-week vacation in Europe after the Watergate documentary airs. She heads down the hall with some papers and instructions for her executive assistant, Francine Proulx. The interview is over. But Dickerson, smiling a perfect-hostess smile, can't resist a parting shot:

"The emeralds," she says, "are real."