NEW YORK - The bad tidings just get deeper and darker for Mayor Rudolph W. Giuliani.
Three months ago, he was a favorite in the nation's hottest US Senate race, which - had he won - could have placed him on track to the White House.
Now, his friends and foes wonder whether Giuliani, a Republican, has a political future at all.
The latest splash - a new book that paints his late father as a Mafia thug and challenges his own claims about his accomplishments as mayor - intensifies the riptide.
There was the quadruple-whammy of May - in which he announced he had prostate cancer, revealed he had a mistress, saw his wife tell reporters that their marriage had been destroyed by his earlier fling with a City Hall aide, and finally withdrew from his Senate campaign.
Before that, his insensitive handling of the police killing of Patrick Dorismond - coming on top of his tepid response to the police killing of Amadou Diallo - tainted his crime-fighting legacy.
''I wouldn't wish the year he's had on anyone,'' said George Arzt, a Democratic political consultant.
The new round of scrutiny set off by the book - ''Rudy! An Investigative Biography of Rudolph Giuliani,'' by Village Voice reporter Wayne Barrett, due to hit stores tomorrow - comes as the mayor appears to be less powerful and prominent than at any time in his six years in City Hall.
Edward Koch, who was voted out of office in 1989 after three terms as mayor and knows what final days are like, said Friday, ''People, when dealing with a lame duck, have no problem stepping on his webbed feet. They don't fear retaliation.''
When Giuliani leaves office at the end of next year, he will be the first New York mayor to be forced out by a 1995 law that limits all elected city officials to two terms.
A well-known politician, one of Barrett's sources for the book, said, ''So many people spoke out because they fear the mayor less as his administration spirals to an end.
''The mayor was a very intimidating figure,'' he added. The lashings against him now are due, in part, to the ''pent-up irritation at the fearful hold he had, where no one could say anything without triggering his wrath.''
Many times, Giuliani has fired employees, held back city contracts, or threatened reprisals when someone was caught criticizing him or stealing too much of the limelight.
''Keep in mind, this is a guy who says he's seen `The Godfather' something like 80 times,'' one former political insider said. ''He learned from that movie. He's governed through respect and fear.''
Now, just as his secrets are spilling out and his days of power are numbered, the fear is starting to subside.
Two weeks ago, as Giuliani was getting ready to give a speech in the Riverdale section of the Bronx, his staff called an Italian restaurant in the neighborhood to make dinner reservations for his entourage - about 20 people.
The restaurant's owner, Charles LaPresto, refused the request, saying he found the mayor ''morally objectionable.''
A Manhattan lawyer, whose clients have experienced Giuliani's wrath, laughed when he read about it in the Daily News. ''Six months ago,'' he said, ''this poor guy would have been up to his eyeballs with city health inspectors, tax auditors, cops who won't answer his call for help if he's robbed.
''I wouldn't have refused the mayor,'' he said before he paused. ''If this guy gets away with it, maybe we all can.''
On the other hand, even now, most of Giuliani's critics will talk about him only on condition of anonymity.
Norman Siegel, the head of the New York Civil Liberties Union and a persistent thorn to Giuliani, said of the mayor, ''He's not as dominating, not as visible as he used to be, he's less of an imposing figure.''
However, he added, ''I've had people in the past who were unprepared to sign their names to a letter criticizing the mayor, fearful that funding for their organizations might get cut.
''These people,'' Siegel said, ''are still afraid to sign their names.''
Arzt agreed: ''If you're asking if it's time to write his political epitaph, the answer is `No.'''
Many political insiders - Democrats and Republicans - also doubt Barrett's book will have much long-term impact on Giuliani's image or future.
Still, two prominent Republicans said the revelations might have hurt had Giuliani stayed in the Senate race. He would have had to answer the charges rather than brush them aside.
''The issue wouldn't be that he had mob relatives,'' one insider said. ''It would be the hypocrisy that the fact highlights.''
Some saw hypocrisy in the mayor's response last week to Barrett's disclosure about the Mafia past of his father, Harold. ''My father died 19 years ago,'' Giuliani said, ''and the details of his life died with him.''
One Republican adviser gasped, ''I couldn't believe he said that, given the Dorismond situation.''
Dorismond, an unarmed security guard, was killed in March by an undercover police officer who mistook him for a drug dealer. Giuliani's popularity tumbled when, instead of apologizing, he released court-sealed records from more than a decade ago showing that Dorismond had committed a crime as a teenager.
Even the New York Post, normally a strong Giuliani supporter, criticized the mayor. A cartoon Thursday shows Giuliani standing in front of two tombstones - his father's and Dorismond's - and saying, ''Do yuh mind Patrick, I'm trying to talk to my dad!! As I was saying Pop, the details of your life died with you.''
