All Night Long : For some people--because they work late hours or because they simply can’t fall asleep--it’s their time to play, relax, hang out.

Neighborhoods, crammed from dawn to dusk with traffic, slowly transform by the middle of the night into ghost towns, one as gloomy as the next. Mini-malls and evening hangouts, noisy and crowded just a few hours earlier, now look sad and neglected.

It must be bedtime for the San Fernando Valley.

By this time--midnight to 6 a.m.--life is unofficially handed over to those who make their own rules. Because they work late hours and need somewhere to unwind before heading home or because they simply can’t fall asleep, the night becomes their time to play, relax, hang out. (Nationally, according to the U. S. Bureau of Labor Statistics in Washington, about 15 million people work at any point between 5 p.m. and 6 a.m. And about 35 million across the country suffer from chronic insomnia, the American Sleep Disorders Assn. in Rochester, Minn., reports.)

“Some people have the Kiwanis Club,” said Colin Liebich, whose flexible hours as a classic car builder allow him time to hopscotch from one early morning coffeehouse to another. “These people have the night.”

And not much else. The Valley, reflecting most of America, is partial to people with 9-to-5 routines. Most restaurants and nightclubs close by 2 a.m.--the law prohibits the sale of liquor any later. Darkness precludes most leisure activities.

But, insomniacs and swing-shifters, rejoice! The Valley does show a pulse in the middle of the night. Almost every intersection, it seems, has either a 24-hour doughnut shop, a convenience store or a Kinko’s, and some restaurants, such as Denny’s and Jerry’s Famous Deli, maintain a consistent following throughout the night. Plus, pool halls stay open well past midnight. Here are a few other signs of after-hours life:

Newsstands

Even brisk winter temperatures can’t keep the night owls away from one of their most cherished pastimes--browsing through all-night newsstands. Patrons often linger for hours, shuffling from one magazine to another, which doesn’t escape the perturbed proprietor when he fails to make a sale.

“I really resent it when people come who clearly don’t have money and aren’t going to buy anything,” said Ron Royce, who works the Friday and Saturday graveyard shift at the 24-hour newsstand at Van Nuys and Ventura boulevards in Sherman Oaks, a Valley institution since 1948. “And you can just tell who these people are.” (The Valley’s only other all-night newsstand operates at Van Nuys and Victory Boulevard in Van Nuys.)

Royce isn’t fazed by anything that happens at his corner. One night, Sly Stallone dropped $140 on a few dozen magazines. Royce offered to give Stallone the publications free if he could guess the exact total price. He couldn’t.

“We don’t make a big deal out of the celebrities who come here,” Royce said. “We try not to be star-struck.”

One early morning regular, if no star, is Pete Demetriou, a radio news reporter for KFWB (980-AM) in Hollywood. Demetriou, who usually finishes work about 12:30 or 1 a.m., sees the newsstand as an ideal spot to gauge subtle shifts in public opinion. He’ll hang out for several hours, debating topics ranging from gun control to fiber optics. Royce warns not to get Demetriou started.

“This is a magical place,” Demetriou said. “I always get into some great conversations here. I’ve started with someone at 1 a.m. and, suddenly, it’s 4 a.m. The people are very intelligent and very eclectic.”

They are also, apparently, very interested in sex. Pornography dominates as the most popular early morning purchase, Royce said. He said he is always amused by the not-so-secret strategy of the embarrassed buyer.

“They’ll place the porno magazine on the bottom of the stack they buy,” Royce said. “Or they’ll say they’re getting it for someone else. . . . I really don’t care.”

Bowling

Finding a free lane during late afternoon or early evening hours is difficult; the Valley is flooded with leagues. By the time a lane opens, the alley is about to close.

Not at Canoga Park Bowl, which never closes.

That’s what attracted Dennis and Kay Shawe one recent morning.

“We were up and we wanted to bowl, and this is the only place,” said Dennis, 38, of Century City. The Shawes arrived shortly before 1 a.m., and bowled five games apiece before going home nearly three hours later. “I guess we wanted to do something crazy.”

Tom Montoya doesn’t think that it’s so crazy. Working the desk from 1 to 9 a.m., he said he is never surprised by the steady flow of bowlers paying $2 a game to attack the helpless pins. Some mornings, half the alley’s 32 lanes are occupied.

“A lot of people get off work at 2 or 3 in the morning,” Montoya said, “and there’s not much else to do at that hour. The bars are closed, so why not bowl a game or two? . . . I get all kinds of people here, from the clean kind who have real jobs to the scuzzballs who only come out at night. Some people come here at midnight and don’t leave till 4 or 5.”

Shortly after 5 a.m., there’s a shift.

“For serious bowlers, that’s a good time to practice,” Montoya said. “They’ll come in here early before they go to work.”

Bowling isn’t the only option at Canoga Park Bowl. The pool tables and pinball machines are often just as popular.

“We’ve got seven pool tables and usually at least three or four are being used,” Montoya said. “Tonight, some guy spent hours pouring quarters into the pinball games. He kept coming here for change.”

Exercise

Michael Sasevich, a USC senior, detests the noisy, early evening workout scene at most Valley fitness centers, each body trying to outperform the next. So, several times a week, he visits Nautilus Aerobics Plus in Studio City shortly before 2 a.m. to jog on a treadmill for half an hour and to lift weights.

“This is a great time for me to be with myself,” he said, “instead of being distracted by all the people who come to clubs.”

He isn’t the only one who has discovered the best time to build up the body. Bob Clinton, a North Hollywood mortgage banker, said the early morning workouts blend perfectly with his work schedule.

“You have to fight for equipment if you’re here much earlier,” said Clinton, 35, who stops at the club three times a week between 2 or 3 a.m. He then goes home to sleep, and starts work about 2 p.m.

The after-hours scene is primarily made up of men. Women, club workers say, don’t feel comfortable about going on the streets during those times. When they do show up, an employee makes sure they get to their cars safely.

The club slows down significantly after 2 a.m., but by 4:30, the first sign of serious activity emerges.

“You get all these stockbroker types who bring their garment bags with suits in them,” said Randy Buenaflor, who works at the club. “They go right from here to work. At 5 a.m., everything starts to fill up as the aerobics crowd gets here.”

Outside, on the roof, the club also offers a T-shaped Jacuzzi. Despite the cold breeze during the winter, “you’d be amazed at how filled it can get,” Buenaflor said.

The center, however, closes at midnight Friday and Saturday evenings, figuring that most people prefer more traditional forms of night life on weekends. Even exercise fanatics need somewhere to show off their hard work.

Coffeehouses

Until 2 a.m., the Valley boasts plenty of clubs offering musical alternatives, from bluegrass to blues. Once the clubs close, however, especially on Friday and Saturday nights, the coffeehouses become more crowded.

Most prominent among the late-night crowd is the Insomnia Cafe in Sherman Oaks, open till 3 a.m. weeknights, and 4 a.m. Fridays and Saturdays. Until closing, the place is usually packed.

“This is where they come to sober up,” a cafe employee said. “A double shot of espresso will wake them up.”

The Insomnia is no palace. The grungy couches and chairs look as if they were imported from Goodwill; the artwork on the walls--paintings depicting scenes of poverty--isn’t quite ready for the Louvre.

But the crowd, mostly in their 20s and 30s, has no complaints with the atmosphere. The idea is to relax, not revere.

On most nights, they remain isolated in their own cliques, absorbed in casual conversation or intense competition. The cafe supplies such games as Monopoly, chess, backgammon and Scrabble.

For Kris Sanchez, revenge was his top priority one recent night. Sanchez, 18, had lost a Monopoly game to his girlfriend, Stephanie Levinson, a week earlier and was determined to make up for the disgrace. “I’m killing her,” said Sanchez, staring at his impressive row of hotels.

Sanchez and Levinson, 19, said Insomnia is the perfect environment to cap an evening. Both go to college during the day and work at night. After hours are just about their only hours together.

“No one bothers anybody else here,” Levinson said. “It’s not like a club. I wish it were open 24 hours. We’d probably be here all morning.”

The Iguana Cafe in North Hollywood, open till 3 most mornings, enjoys a similarly devoted clientele. Poets and musicians experiment with their latest material.

“If you find yourself stuck,” poet Erica Erdman said, “you book a show. It forces you to write.”

Erdman says Iguana is a convenient place to stop on her way to work at Federal Express at Los Angeles International Airport, where her shift starts at 4 a.m.

“We all know each other here,” Erdman said. “We’re up at crazy hours, and this gives poets a place to hang out.”

Another favorite is the Boom Boom Room in North Hollywood. Dimly lighted, the cozy interior also showcases old and used furniture. Soft jazz sets a relaxed tone.

Jean-Louis Strangis and Rick Kaylor sit in the corner, reading newspapers and planning their breakthrough on the Hollywood scene. They have been working on a screenplay, a psychological thriller that takes place in a bomb shelter.

“When you are under pressure all week long,” Strangis said, “you need somewhere to relax in the middle of the night. You can talk to people here, or just sit alone and do nothing.”

The partners meet frequently at Boom Boom to tinker with the script, although they insist that they are not pretentious. Unlike other aspiring writers, they don’t bring their laptops to the cafe.

“Some people come here so they can be seen to be writing,” Kaylor said. “You wonder what they’re really typing.”

Tanning

Who needs the sun, anyway?

Certainly not the tan-seekers who make regular visits in the middle of the night to the always-open Supertans in Canoga Park. Indulging in either 10- or 20-minute sessions, customers pay $2 a crack--the shop calls it the “Happy Hour” special--to recline to music of their choice as the Bellarium bulbs tan them.

“Some come to tan and some come just to relax,” said Jeff Haldorson, who works the counter five nights a week. Typically, from midnight to 3 a.m., several dozen show up. “They listen to the music and tune out the world.”

Michael Lombardi and his girlfriend, Lisa Hantgin, take nightly treks to Supertans. Lombardi, who plays guitar at the Stovepiper Lounge in Northridge until about 1 a.m., said he uses his tanning time as a way to calm down after an intense night on stage. He feels guilty when he misses one evening.

“It’s very addicting,” said Lombardi, 29, of Reseda. “If I don’t go for two or three days, it feels like you are losing your tan, although that’s not really happening.”

Also, women don’t feel threatened by either the late hour or the potential clientele.

“It’s not like anyone will get hurt here,” said Jennifer Fuglevand, 20, of Woodland Hills. “The tanning makes you feel good about yourself. It’s a lot like laying in the sun, and it’s cool to be here in the middle of the night.”