Southland Summer : Lifestyles: Assorted approaches to being cool in the sun greet a new season.

In a city that seems to have no seasons, summer might be expected to pass on by like every other part of the year--a few degrees hotter, perhaps, but otherwise just another uneventful stretch of time.

Instead, the onset of summer--which starts today--triggers a multitude of programmed responses in Angelenos that simply do not compute in any other part of the year.

Natives flee, replaced by strangers who cannot fathom why anyone would ever want to leave. Freeways grow even more crowded than usual, yet traffic appears to be thinning out. Cats become amorous--loudly amorous. The strains of “Lady of Spain” can be heard throughout the land, as more than 2,000 accordion fanciers begin weeks of practice for an annual midsummer competition.

And home cooling specialists brace for summer’s seasonal mad rush for air conditioners--an odd impulse in a population renowned for embracing the heat of the sun.

“I can’t explain it,” says Dave Kahn, a Northridge air-conditioning contractor. “You’d think people would have everything ready before summer hits. You figure it out.”

There is no figuring it out.

The coming of summer can no more be resisted than the sway of tides. How else to explain the seasonal activities of Lee and Sally Lazar. Every year, in late June, as soon as they can depend on a steady supply of sunshine, the retired hardware store owner and his wife remove a brown-and-white striped cafe table umbrella from the closet in their San Fernando Valley condominium and erect it in their yard, a postage-stamp-sized swatch of earth outside their postage-stamp-sized living room.

For the next several months, on Sunland Boulevard, in Sun Valley, the Lazars will while away the hours--sun worshiping in a yard barely big enough to accommodate both of them.

“It’s not like we have enough land to garden or anything like that,” said Lee Lazar. “So we like to sit back and get a little tan.” He is careful not to sit back too far.

At Le Petit Four, one of a half-dozen outdoor cafes that line either side of Sunset Boulevard in a pricey shopping section of West Hollywood known as Sunset Plaza, waiter Alexander Nicholas, 30, expects subtle seasonal changes among his customers.

“Of course, they will be eating lighter--salads and iced tea and those sorts of things,” Nicholas said. And despite the hoary old summer warning against wearing black--dark clothes absorb sunlight, so the saying goes--Nicholas said he would not be surprised to see his beautiful customers showing up wearing black T-shirts and black shorts.

“People always want to make a fashion statement,” he said.

Some of Nicholas’ regular customers may well be jetting off to exotic vacation spots. But they are invariably being replaced by a new and less-fashionable group of diners--tourists. Last year, about 6.9 million visitors wedged into Los Angeles in June--the biggest month of the year for tourism.

Many of those visitors get around in cars, a fact that may help explain the sudden increase in traffic every summer on Southern California highways. According to Gary Bork, Caltrans’ chief of operations, “more people travel over each 24-hour period in the summer than they do the rest of the year.”

Yet, oddly, most commuters--Bork included--would claim that traffic seems to thin out during summer days. They’re right; according to Bork, Caltrans surveyors have noticed that rush-hour traffic volumes on the region’s highways usually decrease by as much as 4% in the summer.

“The traffic is just spread out more,” he said. “You’ve got people off on vacation who aren’t there commuting at the same time every day. You have tourists who spread out their driving all through the day. And you don’t have all those school kids who go to class at the same time every day.”

As summer progresses, the traffic seems to spill from the freeways into the region’s municipal swimming pools. This week, Los Angeles Parks and Recreation Department workers have been working full-tilt to ready the city’s 55 outdoor pools for hundreds of thousands of youngsters. Mechanics have been filling pools requiring as much as 500,000 gallons and checking out daunting networks of pipes, chlorine systems and filters to be certain that the pools are functional before Saturday’s opening.

Recreation workers are careful to refrain from filling pools not ready to receive swimmers because of mechanical breakdowns. This precaution is taken, said city Seasonal Aquatic Director Ricardo Vera, because young swimmers are so eager to get wet that they have been known to ignore warning signs, scamper over locked gates and dive into any pool that contains water.

“I guess it’s the heat,” Vera said.

Heat is also the explanation, city Animal Regulation Officer Donna Smith said, for the explosive growth each summer of the kitten population at local animal shelters.

“It’s the height of the cat season,” she said. “There’s a lot of breeding going on and people are bringing in kittens they don’t have any room for. There just aren’t enough homes for them.”

The seasonal fluctuation in feline hormones can also be a source of unwanted noise pollution in some neighborhoods. “It’s horrible,” Smith said. “You hear an awful lot of yowling. It’s because the toms are fighting over the females.”

Noise levels will also be rising in Hollywood, where underground nightclubs that normally operate on weekends for most of the year suddenly start popping up on weeknights. This means that Los Angeles Police Department’s 30-officer Hollywood vice detail will be coming into work later and staying later.

“Summer means we get more of all kinds of alcohol-related crimes,” said Lt. Pete Durham, head of the vice detail. “For some reason, 85-degree nights seem a lot more conducive for sitting around and drinking than the rest of the year. Guess who has to clean up?”

Still, summer provides more than its share of wholesome entertainment.

Over the next two months, 2,000 of Southern California’s hidden fraternity of accordion lovers will be spending summer afternoons and evenings preparing for one of the country’s largest festivals in honor of their beloved instrument--a mid-August competition sponsored by the Los Angeles-based Accordion Federation of North America.

Since 1957, the federation has hosted the competition to “acquaint the public with the good aspects of accordions,” explained federation executive secretary Peggy Milne.

Some contestants, Milne said, come from as far away as New Zealand. Most, however, are from right here in Southern California, a musical capital noted more, perhaps, for the drone of heavy metal guitar than for the giddy lilt of the accordion polka.

“It’s really a happy instrument,” said accordion teacher Elaine Scarry. “Besides, what a nice way to continue a student’s interest after school is out. . . . The competition gives them something to work for. Why, for some of them, this is the biggest thing in their lives.”