In only 15 months Mary Cunningham and William Agee at Bendix Corp. had become the most glamorous and visible corporate team in America. In this, the third part of a series, author Gail Sheehy shows how even with their executive power and personal brilliance, they were cut down by envy and spite.

Gliding through the time zones in the corporate JetStar, a dynamic young chairman on one side of the aisle and his awesomely bright executive confidante on the other, her strawberry blond hair ablaze in the sun at 30,000 feet, his feet up and his shirt open as they discuss the strategy for divesting hundreds of millions of dollars of company assets -- could there be a more compelling corporate fantasy?

Bill Agee and Mary Cunningham of Bendix, one of the most dynamic management teams in America, spent much of last summer flying around the country looking to acquire the technologies of tomorrow. With close to a billion dollars and change to spend, stock-piled from the sale of other divisions of the company, they planned to retrofit the nation's 88th largest industrial firm to become a high technology leader in the 21st century.

They played a fast game of intellectual tennis, these two. Sometimes they played real tennis. So accelerated was everything about this 42-year-old chairman and the rise of his closest adviser -- months out of Harvard Business School and already, at 28, vice president for corporate and public affairs -- that Mary Cunningham felt as if a decade of business experience had been compressed for her into one year. Bill Agee had made her his closest adviser. She had been largely responsible for the major acquisition of a machine tool firm, Warner & Swasey Co. For a strictly raised Catholic girl with a monsignor for a substitute father it seemed too good to be true.

And it was.

The mildew of envy is a living corroding organism in the corridors of power. Bill Agee must have known that jealousies would become more virulent once he violated corporate age norms by appointing a young woman to a high post. Moreover, to create an alter ego out of a woman would kindle whatever latent sexism there was among her co-workers. This was one thing for which Mary Cunningham idolized him. Most people by the time they reach the top of corporate life avoid risks, she had observed. bBeing the youngest corporate chairman of a Fortune 500 company, Bill Agee might have taken a safe low profile. But no. He welcomed confrontation with such issues. The Corporate Spurs

In passionate speeches (mostly written by Mary) he inveighed against tenure. The custom of "earning one's spurs" through experience -- never mind that it might be the same experience for five years -- he saw as the number one killer of entrepreneurial spirit. He believed in promoting strictly on performance. His whole life had been predicated on "youthful Bill Agee, boy wonder." As chief financial oficer at Boise Cascade before he was 30, he rode the crest when that company was the darling of Wall Street as well as its descent to within inches of bankruptcy. In those nine years he too had felt a compression of experience -- "possibly equivalent to 35years," he says.

Agee also believed in total openness. The kids coming along today, he would say, aren't members of a taboo generation. So it was that traveling around in public in the company of his closest adviser came naturally to him.

The two were seen together at the Winter Olympics. Television cameras picked them up sitting next to ex-President and Mrs. Ford at the Republican convention, and again at the U.S. Open tennis matches.

They ran into Mike Blumenthal on that occasion. Blumenthal was the former king of Bendix who had brought Bill Agee into his realm and had even given the younger man his chair when Blumenthal moved into government four years ago as secretary of the Treasury. Acquaintances detected a coolness between the two men even before Blumenthal left Washington. It was not a happy exit: President Carter had ignored Blumenthal's wisdom on the economy to the point of humiliation. When the former corporate titan returned to Detroit, having resigned from his new career in government, his chairman's seat at Bendix otherwise occupied, his marriage in disarray, a cruel stroke was added by Bill Agee. He did not invite Blumenthal onto the company board.

Now Mike Blumenthal was head of the only other major non-automative company in Detroit, the Burroughs Corp. The succession of kings had not gone smoothly. Poison Penmanship

At the U.S. Open tennis matches Blumenthal expressed some surprise at seeing Agee and Cunningham together at a "purely social" event. In fact, they were traveling with a Bendix party and using the occasion to entertain business and political leaders. And as usual, there was a hotel suite with a central meeting room surrounded by separate bedrooms for each of the several senior Bendix executives who routinely traveled with the chairman.

But the simple visual impact of this striking woman and youthful chairman rendered other executives and their wives invisible. These are not slights taken lightly by old turks tamed to corporate life. Some began to fight behind their backs with forked tongues and poison letters.

Mary saw an important issue at stake: Are women senior executives to be denied the chance to function on the golf course and in the locker rooms the way men do? Shall they be prohibited from traveling in an all-male executive party? Only with a chaperone? Perhaps they should be required to marry men who will come along as corporate husbands? Once distinctions by sex start being made the whole matter becomes silly very fast. Not that Mary was without fears. She knew things, in fact, that she wished she didn't.

What the gossips had not seen was Mary helping Mrs. William Agee prepare to survive a divorce. It was 13 years before, at the Aspen Institute, that the couple had first discussed parting. Bill Agee had been waiting until their middle daughter started college and their late-born son turned 10. Diane Agee had been waiting for a miracle.

A gentle, inward person, so shy that others sometimes did not know if she was listening to them, Diane Agee shunned the social-business occasions that are part of the natural ambassadorial role of any chief executive. As the deadline on the Agees' marriage approached, Mary Cunningham tried to build Diane's confidence and help her to prepare on a practical level to use her interests in dancing, or children, or cooking: Why not become a hospital dietician, or a children's dance instructor? On the philosophical level, Mary shared the belief forged by her own experience at the age of 6 when her own family life was shattered.

"The way to repair yourself after a tragedy," Mary told Diane, "is to learn to give to others."

Nor had the wags witnessed Mary, on a trip to Florida to do an on-the-spot speech rewrite for Bill Agee, walking the beach with Kathy Agee -- a scared 18-year-old girl facing interviews for college along with the departure of her father. Mary coached her, and the girl was accepted at Princeton. But when finally the rupture was about to take place, Mary couldn't bear to watch the pain and stepped out entirely. Ambition and Apprehension

That was June. The July morning after Bill Agee mentioned he was in the process of finalizing his divorce, Mary, paralyzed by apprehension, could not get out of bed.

She had rallied for the Republican National Convention in Detroit, where she and Agee gave breakfasts and dinners for one vice-presidential candidate after another. "Agee is showing a sudden excess of political ambition," one invitee observed. He remembered wondering all evening, who was Mary Cunningham? Gal Friday? Gal Sunday morning?

The gossip was now seeping outside the company. Some executives shrugged their shoulders and said it must be filling a real need for people who have to work and can't watch "General Hospital." Rumors spread that Mary Cunningham was about to be given another promotion, her second in four months. Just goes to show, others said, what it takes to get a good Catholic girl into bed.

Anonymous letters turned up in the mailboxes of Bendix board members. They made malicious references to the public appearances of Bill Agee and Mary Cunningham. The fiercest drums announce territorial battles. Though they hadn't yet been heard by Bill and Mary, those drums were beating loudly by last month in the corporate jungle of Southfield, Mich.

Certain members of the Bendix board diagnosed the problem as a minor one of ambiguity. By now Mary Cunningham was doing three or four jobs at once -- in on all the meetings with investment bankers, all the deals, the strategy sessions -- yet her title reflected only a facet of her work: national affairs. No wonder people she and Agee met traveling wondered if Mary was nothing more than a gal Friday. What was needed to defuse the gossip was a title reflecting accurately her contribution to the company.

But this fall had marked a dangerous confluence of events. Mary's promotion came at a time when anxiety was high throughout the company. A major reorganization meant a loss of some jobs, relocation of others and executive shuffling at the highest levels. Executive Exits

The president of Bendix, William P. Panny, had learned he would not be a successor to William Agee. The board felt Panny's aggressive management style was not compatible with Agee's participatory style. What's more, Panny's background and power base was the automotive business, and Bill Agee's game plan called for diversification into high technology. It was a bitter pill for Panny, a larded man of 52 who had played the game according to the old reward system which held out the promise of becoming chief executive officer in one's late 50s as the capstone of one's career. He walked into Bill Agee's office and summarily resigned.

Another disaffected executive in his 50s was Jerome Jacobson. He held the title of executive vice president in charge of mergers and acquisitions, but the actual power he had lost to Mary Cunningham. He too resigned, a wounded veteran. That left an opening into which the board could move Mary as a reward for her high performance: vice president for strategic planning. She would be the youngest such creature on the North American continent.

It was the next day that the anonymous letter-writing campaign against Agee and Cunningham began. An investigation of their relationship must be launched immediately, the letters insisted.

But most of the board members were said to be pleased with the new changes. They would be announced by Agee in the annual employes' meeting. That should air out the gossip, it was felt.

Mary was not so sanguine. Her control seldom cracked, but every so often, turning around sharply to look at her jet trail, she would catch a glimpse of a black hole, a starless, nameless, sinkhole in the sky, and she would feel a magnetic force drawing her towards it, herself dropping through . . .

"The forces you're up against," she told Agee, "are going to look for the ultimate vulnerability of every woman in the minds of most men" -- her sexuality.

But Bill Agee had seldom appeared so self-assured. His company's stock up, his board behind him, his control consolidated with his predecessor blocked and his challengers out, he was very much the young king of a $4-billion empire, sitting on a war chest of $800 million and looking for "new realms" to conquer. It seemed he could do no wrong. Meet the Press

In late September Bendix stock hit an all-time high, presumably reflecting the Agee-Cunningham strategy for divesting the forest products operation at a cool $435 million.

It was the custom of Bill Agee to solicit issues causing discord or anxiety among the 600 employes at corporate headquarters for an airing at the annual meeting. "This is my psychological contract with my employes," he often said. When his solicitors reported that "this whole female thing" was very much on people's minds but a terribly sensitive topic -- perhaps one he should avoid? -- Agee leapt to the challenge.

"Why should I run from that?" he said. "This is one of the issues the managers of the future must address."

Mary, refusing her fears, agreed with him.

The day of the meeting Bill Agee received a call from a Detroit Free Press reporter asking to attend. Several employes who objected to the way Agee was running the company were planning to leak what transpired at the meeting; it would be better, the reporter said, to have him there.

Agee said he'd check with his brain trust. He phoned back to say fine, but the Detroit News would have to be invited, too.

The chairman began his talk with the good news, announcing more success in the tag sale of Blumenthal-era operations and depicting a future on the outer galaxy of technological innovation. He noted the departures of Panny and Jacobson and denied any interest in joining a possible Reagan cabinet. Toward the end of his talk the ears of his audience suddenly grew points.

I know it has been buzzing around that Mary Cunningham's rise in this company is very unusual and that it has something to do with a personal relationship we have," he said. "It is true that we are very close friends and she's a very close friend of my family. But that has nothing to do with the way that I and others in this company evaluate performance. Her rapid promotions are totally justified."

In the tense question period that followed not a question was wasted on the Cunningham matter. Employes had more urgent issues on their minds, such as their own job security. Having been about as wide open as the Idaho sky of his boyhood, Bill Agee was not prepared for the turbulence immediately ahead. Thinking the matter laid to rest, his mind was already planning the next day's flight with Mary to look in on the San Francisco office.

But Mary Cunningham was stopped by the Free Press reporter on her way out of the meeting.

"Do you have a love affair going with Bill Agee?" Louis Heldman asked.

Stunned, Mary replied, "I will not dignify that with an answer."

The next morning speculation about their relationship hit the front page of the Detroit Free Press, and before the JetStar could set them down in San Francisco, the story had moved on the national news wires.

Bill and Mary of Bendix, one of the most dynamic management teams in America, had slammed into a mountain.