Finally, the main event. The pretrial sparring is over, the jury's in the box, and the case of J. Seward Johnson's last will and testament is under way in Manhattan's Surrogate Court. It was hard to find a seat last week as Johnson's widow (the one who inherits $400, maybe $500 million from the Johnson & Johnson pharmaceutical fortune if the will stands), his children (who inherit little or nothing and are contesting), squads of high-priced attorneys, journalists and courthouse hangers-on all crowded into the wainscoted courtroom, hungry for revelations.

Over several months it will all come out, the claims and counterclaims: that the old man was senile, that he was perfectly competent, that his young third wife was a scheming opportunist or a devoted companion, that his children are acting out of charitable concern or out of sheer greed.

In the midst of it all is a small, plump woman in subdued suits and oversized eyeglasses. Nina S. Zagat, 43, was the first witness to take the stand. She was Seward Johnson's lawyer, but what else she was depends on who's offering the description. Like many of the principals in this drama, she plays a role subject to conflicting interpretations.

Scenario A: As argued in court papers filed by one of the children's attorneys, Zagat was an "accomplice" who, in drawing up the megamillionaire's contested will, helped the young wife who allegedly coerced her elderly and enfeebled husband into an inheritance that will make her one of the world's richest women.

Zagat's reward for her service to the mercenary widow, by this argument, is a fortune in commissions and fees. As executor, she would receive at least $6 million, plus three-quarters of a million or more in trustee's fees annually until the death of 49-year-old Barbara (Basia) Piasecka Johnson.

Scenario B: Zagat was a conscientious attorney who, as she testified last week, merely followed the instructions of the ailing but mentally acute captain of industry to leave most of his property to the woman who had brightened his final years. And though Zagat very properly pointed out that Johnson could limit his executors to lower commissions than state law mandates, he insisted that they receive the full amount.

After all, Zagat had for a decade written his numerous wills and codicils, arranged for sales and purchases of everything from airplanes to art, prepared financial statements, acted as his legal trouble-shooter, trusted adviser and friend. Perhaps it was difficult not to contrast this woman, with her Yale law degree, her association with a top law firm and her doting husband and children, with Johnson's own six children, some of whom had shown less career ambition and considerably less marital stability.

And now, according to the scenario presented in court documents by attorneys for Zagat and Basia Johnson, those children are attempting to "loot this estate," though decades back their father had established hefty trusts making each of them megamillionaires themselves. Even the poorest is now worth nearly four times Nina Zagat's fee as executor.

Name-calling and aspersion-casting are expected elements in any juicy will contest, probably increasing in direct proportion to the millions at stake. This one is believed to involve more millions than any ever fought in New York State. It has generated, in the 2 1/2 years since the six Johnson children decided to contest, tens of thousands of pages of depositions, memoranda, motions, affidavits, orders and notices. Not surprisingly, among those paying close attention to the unfolding drama are the city's lawyers.

"Everyone is very aware of it," says one New York trusts and estates specialist. "We know the players . . . and it involves a lot of money; that's always titillating."

Zagat's attorneys -- she and Basia Johnson, "proponents" of the will, are being represented by Sullivan & Cromwell, while the children, or "objectants," have hired Milbank, Tweed, Hadley & McCloy -- have advised her to grant no interviews during the trial. But the voluminous depositions taken before the trial began, supplemented by interviews with friends, associates and lawyers on both sides of the case, offer a look at an unusually intriguing attorney-client relationship.

In the fall of 1963 Nina Safronoff, freshly graduated with honors from Vassar, entered Yale Law School -- an action that, as one colleague points out, "was not something a woman did lightly at the time." There were just 12 women in the class of 167 students that graduated three years later.

Lawyers who knew her then, and now, tend to talk about her warmth as well as her conscientiousness. "She was a mensch, you know what I mean?" remembers Peter Zimroth, a Yale classsmate who is now a partner in Kostelanetz and Ritholz here. "She was someone very warm, very open, a sensitive person. In a law school atmosphere, someone like that is noteworthy."

Her Yale friends went to the wedding in 1965 when Nina Safronoff married classmate Eugene Zagat, known universally as Tim. They now live on Central Park West with their two sons, ages 8 and 11.

Graduating women lawyers faced a less than cordial reception at major law firms in the mid-1960s. "Our classmates would come up to us and said, 'Wait till you hear this one,' " says classmate Betsy Levin, now dean of the University of Colorado Law School. "People said things they wouldn't dare say now."

Nevertheless, after both Zagats were admitted to the New York Bar in 1967, Nina was hired as an associate at Shearman & Sterling, one of the country's largest firms. She has always worked in its individual clients department, a group of about 20 attorneys known to the irreverent as "full-service lawyers for the very rich." Instead of having to consult the firm's divisions for their various needs -- taxes, litigation, trusts and estates -- wealthy clients could bring their problems to a single unit. Zagat, like her colleagues, had several clients, but over the years she began spending more and more of her time working for one in particular.

Zagat was "a very discreet person in a very discreet firm"; her friends knew that "she was always going off to Florence or somewhere on a real estate transaction" but not on whose behalf, one attorney friend says. Only a few years ago did it become generally known that Zagat was representing J. Seward Johnson Sr., son of the founder of Johnson & Johnson, and his wife.

Why Shearman & Sterling did not make Zagat, still an associate after close to 20 years, a partner in the firm was a question that came up during pretrial proceedings. Zagat testified that she was "not surprised" to learn that she would not be offered a partnership.

In certain ways, she had taken herself off that track. A year after being hired, Nina Zagat requested and received a transfer to the firm's Paris office, where Tim Zagat was working for his law firm. They had a wonderful year and a half, Nina taking cooking classes at Le Cordon Bleu, their shared interest in food leading to a mimeographed ranking of French restaurants that was a forerunner to the popular New York restaurant guide they publish today. (They're planning similar guides for Washington, Los Angeles and several other cities.) But it was not the recommended career move toward partnership. Nor did Nina Zagat rotate through the firm's various departments on her return, as future partners are expected to do.

Friends also point out that Zagat began her family at about the point in her career when partnership decisions are made, a choice she thought weighed against her.

But Zagat, an attorney friend says, "was quite comfortable with what she was doing and with her ability to be close to her children . . . Both [Nina and Tim Zagat] have always been interested in things outside the office. Neither of them falls into the category of people determined to work 14-hour days six days a week to make partner."

Remaining an associate with Shearman & Sterling, as it turned out, may prove a decided advantage when it comes to the Johnson will. Zagat had not shared in any of the fees that her client paid the firm for its services. Her salary and bonuses amounted to $102,000 in 1983, the year Seward Johnson died, and to $107,000 the following year. But if the will she drafted stands, her millions in commissions will not be turned over to Shearman & Sterling, as partnership agreements often specify. Because she is only an associate, an employe, she is entitled to keep them.

Barbara Piasecka, who emigrated to the United States from Poland in 1968, is usually referred to as a former chambermaid in the Johnson home -- an accurate but incomplete description that ignores her university degree and graduate study in art. Seward Johnson divorced his second wife and married Basia, as Piasecka was known to intimates, in 1971, when she was 34 and Seward was 76.

Nina Zagat apparently entered their lives that year; among other things, she witnessed, though she did not draft, a 1971 will of Seward Johnson's. She has said that she began representing him in 1973. That involved a variety of tasks. Zagat was called on to help arrange a Sotheby's sale of old masters from the Johnson art collection, to smooth immigration problems when Basia wanted to hire servants from overseas, to help shepherd construction materials for Jasna Polana (the estate the newlyweds built near Princeton) through customs. She acted as counsel to the Harbor Branch Foundation, the nonprofit oceanographic research institute Seward Johnson had founded and supported. She prepared financial reports. In the last years -- after Johnson, dying of prostate cancer, had relocated to Ft. Pierce, Fla. -- Zagat had a power of attorney that allowed her to write his checks.

And, of course, she drafted wills and codicils. Seward Johnson made 22 between 197l and the final one dated April 14, 1983, though Zagat did not work on the earliest. "Mr. Johnson was like a lot of rich people -- their estates and their money are constantly on their minds," says one source familiar with the case. "He rewrote his will every time the tax law changed."

His wills following his third marriage fit a pattern -- they increased the amount left, directly and through trusts, to Basia while decreasing charitable bequests. Harbor Branch Foundation, in particular, was not a beneficiary of his final will, and has retained Dewey, Ballantine, Bushby, Palmer & Wood to represent its interests in these proceedings.

Nor were the six children of his first two marriages given bequests, except for $1 million and a Cape Cod house left to Seward Jr. But that, too, was part of a pattern. Having long ago established trusts for them (trusts that Zagat's and Basia Johnson's attorneys contend would today be worth more than $100 million each had the principal not been invaded), Seward Sr. had consistently directed their virtual exclusion from his wills. Naming Nina Zagat as an executor and trustee, along with Basia and Seward Jr., was also part of the pattern since 1976, when Seward Sr. first wrote Zagat's name into a will in his own handwriting. "I think he admired her competence and professionalism, the fact that she was able to work and raise a family," says a lawyer close to Zagat. "He felt comfortable with her. She's an achiever."

She had also developed, over the decade, a very close relationship with her clients. She visited the Johnsons' homes not only for legal consultations but for birthday parties, social luncheons, even the 1982 funeral of Seward's pet boxer Princie. She and Basia traveled in Europe together on trips that were "part business, part pleasure," a Basia Johnson associate says. They attended art auctions in Monte Carlo, visited Rome, Paris and London. The Johnsons sent flowers and small savings bonds when Zagat's sons were born and gave her a silver plate as a birthday gift; she brought them marmalade she'd made from their Florida oranges. Just before Seward signed his last will, the Zagat family spent a long Easter weekend vacationing, at his invitation, on Children's Bay Cay, an island he owned in the Bahamas.

Friendship between lawyers and clients is common, of course. But Zagat's relationship with Basia Johnson, in particular, will be an issue in the trial. In an affidavit based on information supplied by his clients and others, attorney Alexander Forger of Milbank Tweed portrayed Basia as a shrieking shrew dominating a senile and dying husband, and referred to Zagat as "her accomplice."

Johnson's children believe, Forger wrote, "that the principal allegiance of Nina S. Zagat was not to the aging client, Seward, but rather to her client, Basia, a contemporary, traveling companion and close personal friend whose recompense for loyalty to and support of Basia was the extraordinary compensation -- indeed, a fortune in itself -- that she is to receive as fiduciary . . . "

Arnold Bauman, a partner in Zagat's firm, called that statement "untrue." Zagat has maintained consistently that she acted according to Seward's instructions.

Like any will contest, the Johnson case hinges on "testamentary capacity" -- whether the testator making the will was senile and disoriented or whether, as Donald Christ, Sullivan & Cromwell's lead attorney, put it in his opening statement, "he did what he wanted and knew what he was doing when he did it." The case also hinges on whether Seward was subjected to "fraud, duress, coercion and undue influence." In practice, most wills contested in New York state survive such challenges; few are broken.

The contests can nevertheless be harrowing. Zagat was deposed for 25 days last summer; her deposition runs to more than 3,000 pages. The first witness called, she has been on the stand for two weeks. Even during jury selection she and Basia were in court daily, sitting side by side, watching and listening, Zagat making occasional notes on a yellow legal pad. All of the Johnson children have also been in court for at least part of the proceedings, sitting nearby without looking at or talking to the two women.

Friends describe Zagat as remaining upbeat and optimistic, but weary from the effort of preparing for the much-delayed trial. "Litigation in estate matters involves a tremendous amount of emotion," says Christ, her lawyer. "Everyone involved in it gets bruised a little."

Though Shearman & Sterling could not represent Zagat and Basia Johnson, since its partners and associates will be witnesses, partner Bauman, who has been accompanying Zagat and Johnson to court, says the firm "has complete confidence in Mrs. Zagat and in her participation in the affairs of Mr. Johnson . . . We know that Mr. Johnson regarded her very highly. He was a businessman of acute judgment and he had long experience with her."

But Milbank Tweed has argued in court papers that Zagat should not have done legal work (including wills) for both Johnsons and "was incapable of providing . . . Seward with independent legal representation." Though it is common and not unethical for attorneys to represent both spouses, it is a practice coming under increasing scrutiny. "Attorneys still do it, in cases where everything is harmonious and open," says Robert Taisey, a partner in Windels, Marx, Davies & Ives and past chairman of a state bar association subcommittee on estate and trust administration. "But if there's conflict, it would be prudent to suggest that one or another consult another attorney."

"In this case, there was not the slightest reason to suspect a conflict," says Bauman. Whether the Johnsons' marriage was harmonious or contentious is, of course, one of the issues to be argued in the trial.

The children's lawyers have also argued in court papers that the compensation Zagat stands to derive from the wills she drafted (which by 1981 had removed a previous limit on fiduciary commissions) is "perhaps understandable for a family member" but "highly questionable in the case of the lawyer-draftsman."

By state statute Zagat is entitled as fiduciary to 2 percent of the estate once it tops $5 million, without any ceiling. But Jeffrey Brinck, a Milbank Tweed partner involved in the case, says that "commonly, almost routinely, in very large estates a cap is employed. Otherwise it leads to commissions that greatly exceed the value of any services that could conceivably be rendered. It's just an element of good practice."

Zagat has testified that she informed Seward Johnson on several occasions of his option to limit commissions and fees and that he chose to allow the full, state-mandated amount. (Under his will, Seward Jr. would have received the same compensation had he not opted to join his siblings in contesting. Basia may well waive her commissions, since they come out of what she would inherit anyway.)

"It's the decedent's decision," comments Taisey. "He can direct that the attorney serve at a reduced fee, or no fee, and the attorney can agree to serve or not. If there's nothing said in the will, the presumption is that the decedent expected the executor to receive the amount mandated by statute.

"If it can be proved to have been earned, it is entirely proper. The court will say she's entitled to it," Taisey says. "In the Johnson case, I imagine there are sufficient complexities that an executor would earn his compensation." But any such determination, Taisey adds, can't occur until after the will is admitted for probate and the decedent's assets collected and disbursed. At the final accounting, the court will decide whether the executors earned their fees or not, a finding that in this case could be years away.

For if Seward Johnson's last will is overturned, Nina Zagat and Basia Johnson can introduce the prior will. There are more than enough wills to keep courts busy for years -- and all of them since 1976, when no one argues that Seward was mentally incompetent, name Zagat as executor. There could also, of course, be an eventual settlement. In either case, Nina Zagat seems likely to receive a considerable sum.

And so, of course, will a bevy of other attorneys. There was a quiet chuckle in court last week as Zagat told of reviewing the now-contested will with her client. After greeting each other with hugs, kisses and first names, Zagat and Seward Johnson went over the document "article by article . . . in the way I usually did," she said. At one point, she asked Johnson if he wanted to write a letter to his widow asking her to give preference to the Harbor Branch Foundation in making bequests in her own will.

"Mr. Johnson said 'No,' " Nina Zagat testified. " 'That will just end up with a lot of lawyers.' "