Mid-afternoon on a sweltering Saturday, and the 57-acre outdoor amphitheater is awash with mud and music. More than 170,000 ebullient rock fans (as many as 200,000 by some estimates) are spread out on the slopes of the natural bowl that faces the 250-foot stage.

For these festival-goers, the spectacle that surrounds them is as important as the lineup of acts like The Kinks and Santana, who will shortly take the stage. Mimes cavort through the crowd while mud-caked concert-goers stroll around squirting strangers with water; bands of bug-eyed boys in Blue Oyster Cult T-shirts cruise the hills calling "oo-baby" to women in skimpy bikinis; a drug vendor eels about, offering mescaline and other hallucinogens.

There is an echo of Woodstock here -- the Woodstock Music and Art Fair, as it was known, a festival of peace, love and music held in August 1969 on a dairy farm in the Catskills. The comparison is inevitable. Like that mythic three-day gathering, this one, called US, offers a star-studded bill and a sprawling rural setting, and it has a distinctly bacchanalian flavor.

But there was a magic about Woodstock -- a sense of cultural and political unity -- that US doesn't have. The earlier rock fest was a cultural phenomenon -- a celebration that touched the national consciousness and became the symbol of the peace and love movement in America. It was a logistical nightmare, besides. The 400,000 people who converged on the concert site in upstate New York were often far from food, water and toilets, and the area resembled nothing so much as the site of a natural disaster.

In contrast, US-goers seem to be united by little more than the desire to "party," as they often put it. No musical or sociological statements are being made here; although the festival is billed as a tribute to the cooperative spirit of the '80s, that grand notion seems more like a slogan than an accurate description of the prevailing mood. There is an exuberance here at Glen Helen Regional Park, but it is the same exuberance that would be in evidence at any gathering of rock fans.

For their part, US Festival promoters are discouraging people from viewing this gathering as Woodstock West. "Woodstock was a disaster," says Stephen Wozniak, the 31-year-old self-made millionaire who cofounded Apple computers and who plowed $12.5 million of his own money into US. "Everything went wrong. The logistics were horrible. There was greed, extortion . . . the difference between this and Woodstock is planning."

Wozniak, a placid, amiable sort who favors T-shirts and running shoes, has been planning this festival for a full year -- ever since it occurred to him that it would be fun to assemble a group of first-rate rockers and "celebrate the concept of US and the '80s and working together." He organized a corporation called UNUSON ("United Us in Song") to produce the event, hired the rock impresario Bill Graham, and applied himself to the task of coordinating a Labor Day weekend concert that would run like a computer. Although he provided the seed money for the festival, and he will bear any financial losses, Wozniak declared that the profits were beside the point: "We just wanted to do everything the way it should be done. I put profits out of my head before we even started," he said Saturday.

When it opened on Friday, the festival bore evidence of Wozniak's attention to detail. The 500-acre park, 2,000 feet into the Tejon Pass and about 55 miles east of Los Angeles, had been transformed into a city. A temporary off-ramp had been built from Interstate 15 (and named for Arnie Zink, a retired Highway Patrol chief). Bulldozers had moved 380,000 cubic yards of earth to enhance a natural amphitheater. Twenty-five hundred showers and Porta Potties were brought in, 800 water fountains were installed, a full-fledged field hospital and eight first-aid stations were set up.

To make the happenings on the world's largest rock 'n' roll stage visible to all, two 50-foot video screens were placed on either side of it, and a third was flown in from England (at a cost of $100,000) and placed on top of the stage.

Wozniak didn't stop there, however. He wanted to have "a modern crafts fair" at his new-age festival and a 35-acre computer and technology exhibit (which drew 140 firms, including Atari, Mattel Electronics, Maxell and Hughes Aircraft) blossomed under five air-conditioned tents.

Before the first fans pulled into camp sites on Thursday, UNUSON officials had hired 1,100 security guards, 200 sheriff's deputies, an 1,100-person cleanup team and a fleet of school buses to transport concert-goers to and from the vast parking lot. They had spent about $2 million for the stage, sound and lights; $1 million for advertising, and about $3 million for talent. They invested $10,000 in a two-way video hookup with Moscow, which would enable about 200 people assembled in a studio to view a live simulcast of US. And they lined up 19 major rock 'n' roll acts, including the Police, Talking Heads, The B-52s, Tom Petty and the Heartbreakers, Pat Benatar, Fleetwood Mac, Jackson Browne, and the Grateful Dead.

Despite their efforts, advance ticket sales were disappointing and US promoters revised their ticket purchasing policy to allow fans to buy $17.50 single-day admissions as well as $37.50 three-day tickets. Tickets also went up for sale at a hastily constructed office near the festival gate.

UNUSON officials had hoped to attract 250,000 fans each day, but the crowd was about 100,000 short of that mark on Friday, and 50,000 short on Sunday. Wozniak said he wasn't worried: although he had snatched just a few hours sleep since Thursday afternoon, when his wife Candi gave birth to their first child at the Natural Childbirth Center in Covina, he was exhilarated. "We've planned everything perfectly," he said. "I walked around the concert area and people came up to me to say, 'Thanks for doing this.' It's not a '60s crowd -- it's simpler. I saw people just sitting and staring at the sunset over the lake, and they weren't even doing drugs. They're just having a good time."

On Saturday, when the air is laden with dust and smog and the temperature soars to 106 degrees, the festival-goers are manageable if a bit boisterous. The field hospital treats far more cases of asthma and heat exhaustion than of drug or alcohol intoxication and police report only a handful of arrests, most on misdemeanor charges. The two serious incidents occurred on Friday, when a Santa Rosa man on his way to the festival was killed in a predawn car accident near the park and when a woman was raped in the concert area.

A sweaty, shirtless, sunburned 22-year-old from Riverside who says his name is Dave-O stands in the middle of the concert crowd and waves a liter bottle of generic soda as he says effusively, "It's the people. It's the rock and roll. It's the atmosphere. US means we can all get together to do whatever the hell we want.

"These are happy people. They want love and peace, but it's related to the '80s. The energy's all flowing together."

A casual survey indicates that although some rock fans have come from Alberta or Indiana or Ohio to be a part of the US Festival, the great majority are Californians, like Dave-O. The event draws a large number from the communities closest to San Bernardino. Frank Oliva, a 35-year-old engineer from Redlands, says he hasn't been to a rock concert in nine years, and that "I wouldn't go out of my way to see this. I came out here because this was so close."

As he speaks Oliva is standing in a quarter-mile long queue for a shuttle that will take him to the festival grounds. Although he arrived before noon, he has been directed to the most remote parking lot and will wait in the heat for 30 minutes before he is crowded into a stifling school bus. "The parking situation doesn't make sense," he says. "It's really poorly planned." Phil Courtney agrees. Courtney, 29, is a writer who lives in Corona; he wears a red kerchief and wide straw sombrero, and his face is soaked with sweat. "I wasn't at Woodstock," he says wryly, "but I think we're finding out what it was all about. I was here for the 'groovy experience', but so far it's been torture just waiting for the bus."

Bob Pugh, 20, a student from Amarillo, is downright disgruntled. He disagrees with Wozniak's pronouncement that US is functioning flawlessly.

"I would never come to this again. This smog . . . I waited in line two hours last night for a bus to take me to my campsite, and I'm waiting again. I thought this was going to be a lush, green place, and it's not what we were told -- it's hot, dusty and ugly."

Once inside the festival, however, most concert-goers have fewer complaints. "If this stays this mellow, it will give rock a good name," says 27-year-old Cheryl Nichols, a sales contractor from Laguna Beach. "This doesn't happen every day -- people are a lot more together than they were at Woodstock. They want to make this work."

"US is a good thing," declares Gigi Daleo, a 19-year-old model who says she lives in Tokyo. Daleo is wearing three gold chains, eight rings, a neon-pink bathing suit and pink striped leg warmers. Her eyes are rimmed in silver glitter and she carries a white parasol.

"I wasn't sure what it would be like. I know nothing about Woodstock except the pictures of hippies walking around in the mud. My mother was one of them -- I told her I was coming to this and she said she hoped it would be as good.

"Now that I've seen the people here and I've gotten some attention, I think it looks really great, you know?"

Daleo stands alone at the edge of a clearing where a crowd is cavorting between rows of sprinkler poles. A jaunty guy who has parked an air mattress under the spray is drawing cheers from his cohorts; reclining with his Panama hat pushed down to his nose, he is nursing an orange popsicle and smiling blissfully.

Most of the spectators at the US Festival are white, and most under the age of 40. Although some brave souls have brought children, the family groups are far outnumbered by the hard-partying, unattached, under-25 set. Woodstock-style long hair and love beads aren't much in evidence; while the avant-garde opts for Mohawk haircuts and pierced nipples, the prevailing sartorial style calls for bare feet, gym shorts or bathing suits and one of the 30-odd varieties of US T-shirts on sale.

Souvenir T-shirts aren't the only commodity fans can buy here. Outside the gates, vendors are peddling US and "E.T. phone home" bumper stickers, fruit pops, visors and spray bottles with the festival's rainbow logo. Once inside US-goers can stock up on necessities like suntan lotion, paper binoculars, hats shaped like umbrellas and, of course, food and drink: a beer goes for $1.50, a bagel, $1.

In fact there is a decidedly commercial air about this gathering. Six hot-air balloons shaped like bottles of Miller beer sway gently in the breeze off the lake, and "Fast Times at Ridgemont High" is skywritten over the amphitheater. Datsun has a large striped tent, a win-a-car contest and a hot-air balloon just a bit smaller than Apple Computer's. The stage itself looks like something from a television variety show. The ubiquitous US logo is written across the top in lights and a laser display plays above it when evening comes. The Goodyear blimp is here, as well. On its underbelly is a screen that displays messages like "Thanks, 'Woz' ".

Put it all together, and you have a major sensory overload. But the roiling carnival atmosphere seems to be a part of the attraction. As one sidewalk philosopher standing in the beer garden is heard to say, "This is better than Woodstock, man. It's . . . it's awesome."