LAS VEGAS — On a Sunday afternoon in Las Vegas, at the hottest pool party in town, the Hard Rock Hotel's Jack LaFleur is the man to know. The promotions director stands at the velvet rope, deciding who will shake their booties in the sun — and who won't.

"Only girls, send 'em up!" LaFleur barks as a stream of twentysomething, bikini-clad girls hop the line, leaving a couple of hundred men in their wake. "No more guys. It's out of control."

This is Rehab, Las Vegas' best-known, biggest and craziest pool party. In the 21 Sundays it will operate this year, hotel executives estimate that Rehab will rake in about $6 million — nearly $35,000 every hour it's open. As many as 3,000 tanned and toned bodies find their way into Rehab each week, where they play swim-up blackjack, gulp down $17 cocktails served in 30-ounce plastic jugs and make out under waterfalls, on chaise lounges and, well, just about anywhere.

Since it began in 2004, Rehab has transformed Vegas' daytime scene into a "Girls Gone Wild" tableau of debauchery. Today, almost every major casino resort has nightclub operators managing their 21-and-over pools. They hire DJs to spin music and demand hefty cover charges.

Several resorts have separate "Euro-style," or top-optional, pools, with half-naked girls cavorting in the water.

"It's done a remarkable thing to the nightlife landscape," LaFleur said. "Day life? It's hard to even categorize it. ... It's finding those ways to generate revenue. For a town that's been known exclusively for nightlife, this was extremely daring and off the charts."

By 8:30 a.m., a ghastly hour by Vegas standards, people are already lining up outside Rehab, even though the pool doesn't open until 11. "It's almost like a 'Star Wars' premiere," LaFleur said. "They sit down. They hold that spot in front."

Others, like Lisa Tully, a 38-year-old nursing manager from North Carolina, show up a bit later — and flash a little flesh to guarantee access.

"As soon as we pulled the cover-ups off, they said, 'Bam. Come up here,' " said Tully, who sported a pierced navel and a black bikini dotted with rhinestones.

When it first opened, organizers envisioned Rehab as a place to relax on Sundays after a weekend of partying.

"That lasted about a week," said the Hard Rock Hotel's marketing guru, Phil Shalala. "People were actually beginning to stay in on Saturday night just so they could go to Rehab during the day."

Once inside, people are racking up huge tabs. In addition to the $17 cocktails, Rehab serves alcohol by the bottle. Bacardi rum that retails for about $15 costs $375; a bottle of Jagermeister — typically about $20 — is $400. The big spenders can drop $1,195 for a bottle of Cristal champagne, which normally runs about $300. Roving photographers snap pictures like paparazzi and post them online.

"These people have money in their pocket," Shalala said. "The overall lifestyle that they live is work hard, play harder."

The scene has become so successful so fast that Hard Rock is planning to double the size of the pool area — already 4.7 acres — in the next couple of years. It also will add an upscale, more relaxed setting by 2009.

At the Venetian, the new Tao Beach Club — an extension of the successful Asian-themed nightclub — opened in May with a party hosted by hip-hop artist Jay-Z.

The Venus Pool Club at Caesars is decidedly upscale, offering frozen grapes and frozen towels and charging $650 for a daily cabana rental.

"This is just filling a void Vegas lacked in the daytime department," said Alex Acuna of the Light Group, which operates the new "Euro-style" Bare at the Mirage.

Bare is the smallest pool-party venue in town, and brags about it.

"It's not a spring breaky, 2,000-people pool party," Acuna said. "It's 250 people, intimate. Great music, great food, great drinks, great service."

Unlike Rehab, which serves nachos and chicken fingers, Bare peddles mojitos by the pitcher, lobster tacos with grilled mangos and shrimp lettuce cups.

And although nobody's doing cannonballs into the pool, a battle cry to "release the twins" results in a round of free shots for ladies who go topless.