Perot: Running on Empty : CITIZEN PEROT: His Life and Times.<i> By Gerald Posner (Random House: $25, 401 pp.)</i>

He was the incredible shrinking man.

That was four years ago when the Ross Perot of pop mythology stepped from the sheltered suite of business into the arc light of politics. In no time at all, he was a contender for president. Then he found himself the most ridiculed figure in American public life. A man regarded for his can-do was reduced to crackpot.

For millions of Americans, that is where Perot remains--like residue at the bottom of an overheated saucepan, only a vague and bitter extract of the many ingredients of this remarkable life. Now comes former Wall Street lawyer-turned-journalist Gerald Posner to meticulously reconstitute Perot in time for the 1996 presidential go-round. And guess what? Just about everything you thought, suspected, heard-but-forgot, feared or hoped about Perot turns out to be true.

In Posner’s hands, it’s not an appealing portrait. Still, “Citizen Perot” does make for engaging reading, especially for those who might ask themselves just why in the world they were first so strongly attracted to and then so urgently repelled by the tycoon from Texarkana.

Yes, Perot is a motivator and clean-liver, the likes of which we seldom see these days. And he shares qualities with other quirky but commanding leaders. That is, like Winston Churchill and Ronald Reagan, he holds absolutely no doubts about himself or the rightness of his thinking at the moment. Like Huey Long and George Patton, he regards those who question him as fools and spares no one in his way.

But there is a thin and fateful line between a man of character and one deserving caricature, and in this delicate exploration, Posner is at his most illuminating. Surely Perot is not the first self-aggrandizing, imperious, temperamental, vindictive, visionary and hugely lucky myth-maker to regard himself as the fittest leader in the land. One could easily make the case that these are necessary traits for a president, in measured amounts.

Yet Posner’s unauthorized biography, with which Perot only fitfully cooperated, reveals a man who lacks the requisite dharma necessary to inspire broad trust. A man who seems transparent in regarding not just his enemies but his supporters as fools. Despite Perot’s self-made business wealth, he is presented as someone who stopped learning, or feeling the need to learn, a long time ago. Behind the self-effacing pose is an autocrat who came to believe in his own infallibility.

These are not Posner’s stated conclusions. A classic-style investigative journalist who has written five other books, the author’s strength is in showing rather than telling. Much of what is covered here about Perot’s life is known, at least in outline. Posner’s reporting fills in parts of the picture, often richly and for the worse.

How did Perot get wealthy? Through government data processing contracts, political connections and brutish attacks on would-be competitors--business practices that by today’s standards sometimes cross the line into questionable. He also made himself such an annoyance at General Motors that the company that first bought Perot in as a business partner for $900 million later bought him out for $742 million.

Posner presents vivid scenes: While Perot was telling a news reporter that the GM buyout of EDS, his data processing company, was outlandishly oversized and “morally wrong,” he had his attorney on the telephone demanding to know why the money transfer was 15 minutes late.

Whether such dissembling could have an impact on Perot’s 1996 political ambitions has long been a matter of argument. His supporters tell themselves the public will not resent Perot for having used and even exploited the American system to his own financial advantage--such as promising to help President Nixon with pet projects, for instance, then demanding White House intercession with regulators to assist Perot’s business. By this thinking, a man wily enough to outwit and out-muscle Washington and GM for his own good can just as easily bring the establishment to heel in the public interest, a contemporary twist on the fox-in-the-henhouse fable that tells volumes about today’s values.

The omission in Posner’s reporting is his inability or unwillingness to humanize Perot outside the context of business and political dealings. We learn that the once-austere Perot lifestyle became more opulent as his wealth increased, but the behind-the-scenes man--his passions, activities and behavior--remain almost entirely unpenetrated.

Not so the Perot myths, including the most famous of all: how Perot “rescued” two employees held in prison in Iran on corruption charges as the country slid into revolution in 1979. The Perot-authorized glamorization of the tale became a bestseller, “On Wings of Eagles” by action novelist Ken Follett.

Posner lets air out of this story. Yes, Perot certainly did roll up his sleeves and take action by hiring his own rescue squad and traveling himself to Iran. But he got in the way of American diplomatic efforts to safeguard thousands of other Americans in the chaos and owes embassy workers a debt of gratitude for his own safety, instead of the contempt with which he has treated them.

Posner is best remembered for his 1993 reexamination of the Kennedy assassination, “Case Closed,” a book that sought to debunk conspiracy theorists and supported the conventional conclusion that one gunman, Lee Harvey Oswald, did the shooting. This new book does not go so strongly against the popular grain but enriches much of the standard and critical thinking about Perot.

Perot’s seeming paranoia about people out to destroy him is probed and found to be--mostly paranoia. In particular, the author delves into Perot’s mysterious and temporary pullout from the presidential race in 1992, after supposed “reports” that Republicans were planning to embarrass daughter Carolyn. Posner traces the bizarre and convoluted story to a con man who apparently gained Perot’s trust.

To critics, and even some fence-sitters, one of Perot’s most condescending characteristics is his recurring suggestion that he acts not in his own interests but because voters have appealed to him to save the day. This ploy is unmasked numerous times in “Citizen Perot,” including the moment when Perot decided to run for president in 1992.

The author quotes Perot’s onetime hireling, novelist Follett, for a different perspective: “I’ve heard him say it, ‘If I could run for king, I would do it.’ ”