MIAMI BEACH » In this decadent, hard-partying playground, Kirsty Bertarelli’s 40th birthday celebration rivaled the best of them. More than 200 guests flew in from Europe. A caravan of limousines ferried them to the site, a flashy waterfront home. The party rocked until 4:30 a.m. It cost $3 million.

But the fact that it almost did not happen — that a judge had to decide on the very day of the event whether to allow it — has reignited an increasingly familiar debate here: When does someone’s really good time become the bane of someone else’s existence? Or, in the case at hand, did one billionaire homeowner rent out his mansion for another billionaire’s party, and did that rental violate a local ordinance?

“Kirsty’s Fabulous 40th Birthday Party,” as it was billed, was thrown last month by Swiss billionaire Ernesto Bertarelli, ranked No. 64 on Forbes’ most-wealthy list, for his wife, a singer and a onetime British beauty pageant winner.

It was held on Star Island, a spot of land on Biscayne Bay beautified two decades ago by the developer Thomas Kramer, a lover of late-night bacchanals and no stranger to controversy. Kramer rented his estate, Five Star Island, to the Bertarellis for $40,000, a sum that barely covered his expenses, he said. The day before the party, a routine request to the Fire Department to have paramedics on hand caused the city to review the rental agreement, and then threaten to shut down the affair with a police roadblock.

That led to a court hearing in downtown Miami. At risk were the reputations of the rich and famous, Kirsty Bertarelli’s feelings, the tempers of moneyed, jet-lagged guests, and Miami Beach’s tolerance for the whims of the wealthy.

“My wife’s 40th birthday will be ruined and forever remembered as a public disgrace to my family unless the party goes forward,” Ernesto Bertarelli told the court, via affidavit, since presumably he was busy preparing for the event.

Summoned on a Saturday afternoon for a rare party-related emergency hearing, Circuit Judge Jose R. Rodriguez listened as lawyers explained that the Bertarellis had no idea their one-night house rental was illegal in Miami Beach, a claim that no one disputed. The judge, holding the ordinance to be ambiguous, swiftly dispensed with the case: The party should go on.

The mayor, Mattie Herrera Bower, is incredulous. “If you have enough money, you can get a lawyer to get a judge to break the law,” she said. “And I was unhappy about the precedent. We have a law for a reason, and everybody — even people with money — needs to obey it.”

At the center of the imbroglio is a Miami Beach ordinance that bans using a single-family home for commercial purposes, namely holding parties where money changes hands between the homeowner and the party host. The city passed the ordinance in 2008 after too many mansions were being used as ballrooms-for-hire, jammed with indiscreet partygoers who turned up the music, parked their cars willy-nilly and rankled the Beach’s hoi polloi.

But the law hardly halted the one-night party house rentals; in fact, the listings increased and the parties of out-of-town revelers bobbed below the city’s radar. “During a certain period of the year, every other weekend something was going on: a launch for a vodka company, a launch for an automobile company, promoters with an after-party,” said Jorge Gomez, an assistant city manager for planning and zoning. “Hundreds of cars descending on the neighborhood, valet operations stashing cars all over the place — it really had a big impact.”

At the same time, owners began renting out their mansions for the night, the week or the month, a result, in part, of the drastic economic downturn. A trio of palatial islandson the bay west of Miami Beach (of which Star is one) may bask in the glow of wealth, but that kind of luxury comes at a price. Ten of 34 properties on Star Island are now for sale, a record number, real estate brokers say.

Gloria Estefan lives across the street from Kramer. The estates of Sean Combs, aka Diddy, and Rosie O’Donnell are nearby.

City commissioners banned the short-term rentals of private homes in February 2009, setting the minimum rental period at six months and one day. They said they feared not only an influx of interlopers but also potential damage to the hotel vacancy rate.

But the second ordinance has been even more flagrantly violated, with websites listing dreamy spots with expansive gardens, infinity pools, wine cellars and state-of-the-art media centers. A Miami Beach company, Villazzo, offers short-term rentals of 11 Miami Beach “villas” and “villa-hotels.” One owned by Donald J. Pliner, the shoe designer, is $6,500 per night.

“The problem we have, with all due respect, is the law is not being enforced,” said Hans Mueller, a banker who is a Palm Island resident and the president of the homeowners’ association of Palm, Hibiscus and Star Islands, in an appearance before the city’s land-use and development committee on Feb. 23.

Five Star Island’s owner, Kramer, 53, a German citizen, has violated both ordinances, city officials say. The website for his 11-bedroom, 29,000-square-foot property — complete with brass stripper poles embedded in a long dining room table, a stuffed giraffe head looming over the central staircase and a waterside sauna protected by bulletproof glass — beckons renters and partygoers alike. The property, which features a giant crucifix in Kramer’s bedroom and mini-busts of the Seven Deadly Sins above his bed, is described as “the ultimate location” for weddings, vacations, events, photo shoots, commercials, TV shows and films. Penthouse Magazine shot a video there in December.

When the city obtained a copy of the rental contract for the Bertarellis’ use of Kramer’s house, from 7 p.m. to 4:30 p.m., code enforcement officials pounced on the chance to send a loud message, said Jose Alberto, the code compliance administrator for Miami Beach. But the judge disagreed, and the case is now on appeal.

Kramer said he was unaware of the ordinance barring commercial use of private homes until just recently. He is perplexed, he added, about the stance of city officials. “Instead of harassing me and threatening me with lawsuits, the city should thank me for bringing some much needed revenue and hundreds of new jobs to Miami Beach,” said Kramer, whose investments in the early 1990s helped spur South Beach’s revitalization.

As for the city’s leaders, he had a not-so-gentle reminder: “I bought 16 of the 20 lots on Star Island and transformed it from a trash dump into an exclusive gated community with the multimillion-dollar homes of celebrities.”