Early on a Saturday morning last October, Thomas P. Puccio, the Abscam prosecutor turned New York defense lawyer, arrived at 960 Fifth Ave., an apartment building Puccio describes as "a real big-time place."

The doorman directed him to the eighth floor, where the elevator opened on a vast, 14-room apartment overlooking Central Park. There Tom Puccio, the man federal agents in Brooklyn used to call "The Pooch," got his first look at his most famous client, Claus von Bu low, the Danish-born socialite now on trial here a second time, accused of twice attempting to murder his enormously wealthy wife.

Flanked by two big golden retrievers, von Bu low was wearing corduroy slacks and an ascot. He is tall (6 feet 3), blue-eyed, barrel-chested and continental. His lower jaw juts forward. He has a high forehead and a long, regal nose. To Puccio, von Bu low seemed like a caricature of himself. Rich, suave, rich, cultivated, affected and rich.

"He looked like he was supposed to look. He is a very proper guy," said Puccio, who may get his chance today to confront the elusive Alexandra Isles, who is considered a crucial witness for the prosecution. And later this week, he is expected to begin presenting von Bu low's case as his chief defense attorney.

Fifth Avenue is a long way from the federal building in Brooklyn where Tom Puccio spent 13 years building a reputation as a hard-hitting prosecutor surrounded by drug dealers, notorious landlords and labor leaders, stool pigeons, racketeers, mobsters, crooked cops, sleazy con men and corrupt politicians.

Since he left Uncle Sam's payroll three years ago, Puccio's workdays have been spent, among other things, representing Vitas Gerulaitis, the tennis player and jet-setter; consulting with the Louis Vuitton Co., handbag maker to the well-to-do; meeting in Switzerland with lawyers for oil trader Marc Rich; refereeing a family fight over a big estate in Rochester, N.Y.; and now defending Claus von Bu low and his dangling fortunes.

"I've got a lot of clients who have got a lot of money," said Puccio, including one who he said has $35 million worth of Renoirs on his living room wall.

Of course, Puccio said, that only amounts to about six paintings. As for the von Bu low place, Puccio said, "It's a real nice apartment."

As for von Bu low, "he was just a name, a person in New York. When I met him, I was pleasantly surprised."

The Pooch has gone "uptown."

In April 1984, the Rhode Island Supreme Court overturned von Bu low's conviction on charges that he tried to kill his wife, Martha (Sunny) Crawford von Auersberg von Bu low, with injections of insulin. Sunny von Bu low now lies in a New York hospital, locked in a deep coma from which her doctors say she will not emerge. She is 53 years old. Claus von Bu low, 58, expecting to face a retrial, was looking for a new lawyer.

At the first trial, which resulted in von Bu low's being sentenced to 30 years in prison, the lead defense attorney was Herald Price Fahringer, a formal, self-confident and suave Park Avenue criminal lawyer whose manner was very much like von Bu low's. Maybe too much.

For the retrial, von Bu low wanted somebody different, not a von Bu low clone, but somebody feisty, somebody who understood how law enforcement worked, somebody more like Stephen Famiglietti, one of the state prosecutors who convicted him.

"I wanted to take a prosecutorial stance, as opposed to a defense posture," von Bu low said one day last week in the courthouse here, where he was reposing on a corridor wall, smoking a cigarette. Von Bu low said he met with Washington lawyer Edward Bennett Williams but that Williams "was not prepared to take on the case personally." Williams is a great guy, von Bu low said, but there would have been the messy problems of shuttling back and forth from New York to Washington and the delegation of work to other lawyers, which von Bu low didn't want.

Von Bu low had a long list of candidates, including Tom Puccio. He had heard a lot about the Abscam prosecutor, he said, and Harvard law professor Alan Dershowitz, who was von Bu low's lawyer on appeal, was a fan of Puccio's. Von Bu low called him up.

"I want to meet you and look in your eye," Puccio said von Bu low told him. During their meeting at 960 Fifth Ave., Puccio, who was wearing "a sport coat, tie, something like that," joined von Bu low in a breakfast room where they ate "just croissants, coffee, that sort of thing." They were served not by a butler or maid (they have been let go) but by Hungarian-born Andrea Reynolds, who shares the apartment with von Bu low.

Von Bu low "sat down and launched into a three-hour dissertation of his case, which is what most people do. I for the most part listened," Puccio said. "He impressed me."

A few days later they met again for dinner at Bravo Gianni, a favorite Italian restaurant of von Bu low's on Manhattan's Upper East Side. And a few days after that von Bu low hired him.

"There were a few things I had to get out of the way; then I cleared the decks, for this," Puccio said.

Since then, Puccio added, "Claus has been a pretty decent guy to represent." When von Bu low was asked at the courthouse last week if he wanted to talk about the price tag on his defense, he said curtly, "No. Not at all."

"A substantial amount of money" is all that Puccio would say during an interview last week at a local restaurant. "I've never discussed fees," said Puccio between sips of a white wine spritzer. Puccio said that the matter of fees came up at his first meeting with von Bu low. "Claus is a very meticulous guy." Von Bu low accepted Puccio's fee "and that was it," Puccio said.

Puccio, who was earning $57,500 a year when he quit the government in 1982, said, "I've charged as much as $300 an hour. I've charged more than that." Sometimes, he said, he charges on a "per phase" basis (phase of the case, that is) and sometimes he just sets a flat fee, which is what he did for von Bu low.

"I'm very good at setting fees," said Puccio. "I'm also very good at collecting fees. I've never been stiffed by a client."

His technique? "Very simple," he said. "In advance."

Thomas Philip Puccio, 40, was an only child, raised in Brooklyn and graduated from Fordham University in the Bronx. His father was a purchasing agent with the United Nations and later with the government, and his mother was a secretary at an advertising agency. In college he majored in English. Afterward, "the prudent thing to do was to go to law school because you couldn't make a living writing poetry, as one of my more educated cousins told me."

In 1969 he earned his degree from Fordham Law School and joined the U.S. Attorney's Office in the eastern district of New York. There is a certain breed of young lawyer that becomes a successful prosecutor there and Tom Puccio was one of them.

He was tireless, bold and totally focused on his work, according to his close friend Jack Newfield, a senior editor at The Village Voice. No one would call Puccio a legal scholar, but he knew how to apply the facts to the law. And he had what one defense lawyer described as a combination of aggressiveness and arrogance that has become "a high art" in the New York Federal Prosecutor's Office.

While he was in the U.S. Attorney's Office in Brooklyn, Puccio won convictions of police officers accused of stealing the so-called French Connection heroin from a police property room. Because he was so entrenched in the work, it was necessary, during one of those trials in 1976, to have a Brooklyn official open the local marriage license bureau early one day so Puccio could get the paperwork he needed for his wedding. He and his wife Carol Ziegler and their 6-year-old son Matthew live in Brooklyn Heights where a big campaign picture of Bobby Kennedy hangs in the living room. Newfield said Puccio can cook great Italian meals and is a fan of Billy Joel.

In the courtroom here, where Puccio takes his place next to von Bu low every day, he appears fidgety, impatient and ever eager. Slumped in his chair, his right shoulder hunched up, he fiddles with his upper lip, the tip of his nose, his lapels. He examines his fingernails. He is not nervous, he just has a hard time waiting his turn.

He wears large, clear-rimmed glasses with lenses that make his almond-shaped eyes look large and filmy. The top of his head is bald except for a few long strands of hair that are combed up from one side. And he is well dressed, but doesn't match his client's tailored suits, ornate buttoned cuffs and fancy pocket handkerchiefs.

Puccio's manner outside the courtroom is friendly and often amusing, although he frequently seems distracted. He wastes no time on charm or finesse.

"Tom has only one gear . . . overdrive," said Irving Nathan, a partner in the Washington law firm of Arnold & Porter, who was deputy assistant attorney general at the Justice Department when Puccio was supervising the Abscam cases. At the time, Puccio was director of the Federal Organized Crime Strike Force in Brooklyn, a job he had taken over in 1976 when he was 32.

There was no love lost between Puccio and the defense lawyers who represented the members of Congress who were convicted of taking bribes from FBI men posed as Arab sheiks. Some are still festering over their losses to Puccio, who led the prosecution in four Abscam trials. Some praised him for his courtroom abilities, which included healthy doses of ridicule directed at the cornered congressmen, and his investigative tactics were sometimes described as creative. Others called those same tactics entrapment. Some said Puccio thrived on the limelight and anticipated a lucrative book deal with his friend Newfield. No book has been written.

"I was offered extravagant sums of money just to talk to someone for a couple of weeks who would then write a book. I would never do it," Puccio said.

Anyway, Puccio said, "I think if you write a cookbook, you have a better chance of being read than if you write about the Department of Justice, so maybe I should write the Abscam cookbook."

"He had all the personality of an affidavit," said Abscam defense lawyer Michael Tigar, who fought it out with Puccio over the charges against former representative John Murphy of New York.

"This may sound strange to you but I never thought I developed a prosecutor's mentality," said Puccio, who was considered one of the most controversial federal prosecutors in the country. "I only brought cases I believed in."

Within the network of prosecutors' offices involved in the Abscam cases, Puccio had his share of critics, including two New Jersey prosecutors who wrote a nasty memorandum forwarded to Washington claiming that Abscam undercover con man Mel Weinberg had run amok. And there were mean bureaucratic turf battles about where the Abscam cases would be tried. Puccio, his critics say, wanted to hog all the action in Brooklyn.

So when Tom Puccio was asked if he looks back on Abscam as the good old days, he was not ready to agree. He took a lot of heat for Abscam, he said. And he added, "It just got to be annoying after a while to hear the same tired arguments about Abscam . . . I didn't discover Abscam. I didn't think up the idea."

In May 1982, Tom Puccio ended his career with the government. A few months earlier, the Justice Department had sought him out as a possible candidate for U.S. attorney in either Washington or Miami, but he did not pursue either job. Puccio, the man who once said that he could indict a ham sandwich (the real issue, he says, is can you convict one?), said, "I'd had enough of being a prosecutor."

He joined the Park Avenue law firm of Booth, Lipton & Lipton to which he had been introduced by his friend Mario Cuomo, who was then New York's lieutenant-governor. Puccio said that "All I remember about the first three months of private practice is having lunch," adding that he used to tell people, "I used to practice law, now I practice lunch."

Within a year, he left Booth Lipton and opened his own firm across the street. In April that firm was dissolved and Puccio, who didn't like the constraints that law firm management put on his work, became a partner in the huge New York law firm of Stroock & Stroock & Lavan. He has been so tangled up with the von Bu low case that he has yet to set foot in the firm's offices.

"I've never done anything as a defense lawyer that I would have criticized as a prosecutor," Puccio said. Not even when he scooped a New York grand jury and announced to the public that his client, tennis player Gerulaitis, was about to be indicted in connection with a drug investigation. He then held a press conference to explain Gerulaitis' side of the case.

"It was a preemptive strike on the prosecution through the media," said Puccio, who at this point was trying hard to conceal a mischievous grin.

"My intention was to let the grand jury know what the case was really about," Puccio said. Grand jurors read newspapers and they watch television. A month later, the New York Prosecutors Office announced that the grand jury had decided not to indict Gerulaitis.

"It was a very interesting maneuver. It was totally within the rules," Puccio said.

Would he have been angry if a defense lawyer had done that to him when he was a prosecutor? "Well, I don't know," he said, "I think what I did was fair."

When you are an out-of-towner in a Rhode Island courtroom, as Tom Puccio is, there is a code of conduct that must be learned right away -- don't step on the toes of the locals. Confrontation is frowned upon and extreme deference, which includes bowing to your adversaries while you are politely attacking them, is the rule. Tom Puccio, who is the product of the go-for-it school of law, has made the necessary adjustments.

"You're one step ahead of me as usual, your honor," Puccio said to Judge Corinne P. Grande one day last week.

"That sounded like something Mr. Sheehan would say," replied the judge, referring to John Sheehan, a longtime Providence lawyer who worked with Herald Fahringer on the first von Bu low trial and who remains a member of the defense team.

"I'm practicing," Puccio told Grande.

As for Sheehan, he demurs when asked about his relationship with Puccio, resorting for a response to paraphrasing Shakespeare.

"I'll give my thoughts no tongue," he said.

The von Bu low trial is played out every day here on the fifth floor of the state's red brick courthouse on College Hill. A few blocks away, on the 14th floor of the Biltmore Plaza Hotel, the defense has set up camp in several large rooms. One is used as a storage closet for dozens of cartons of transcripts and legal documents from the von Bu low case and for a Canon copier.

Next door there is an IBM computer that is plugged into Lexis, a valuable -- and expensive -- data bank of legal cases. And there is a portable videocassette recorder that the defense sometimes uses to tape portions of the trial, which is broadcast each day by the Cable News Network.

The defense's medical library is located in Puccio's suite where a bookshelf is filled with such tomes as "Principles of Neurology" and "Diabetes Mellitus."

Von Bu low, who is staying on the same floor of the hotel, comes in every morning at 8:30 for coffee with Puccio and he stops in every night.

Did he do it? Did Claus von Bu low twice inject his wife with insulin, intending to kill her so he could inherit millions and marry Alexandra Isles?

"I wasn't there, but I don't think so," said Puccio.

"I believe von Bu low is innocent of these charges. That is as far as I want to go now."

It was late Friday afternoon. Puccio stood in his hotel suite huddled in conversation with von Bu low. After a few moments, von Bu low said goodbye and left the room. It had been a good week for the defense and von Bu low had said he was feeling confident.

Puccio, who is not one to assess wins and losses before a trial is done, waited for the new week to begin.