For thousands of people, picnicking is as much a part of summer as traffic jams at the beach.

The sun was shining, the breeze was rustling the tall trees, and the afternoon warmth proclaimed that summer has come to the South Bay.

In Manhattan Beach’s Polliwog Park, three women and their small children were enjoying one of their favorite pastimes--picnicking in the park with sandwiches, cheese, fresh fruit and, to the kids’ delight, crackers and peanut butter.

For the women, who met at a child-observation class, picnicking with their youngsters is a regular event.

And sprawling Polliwog Park--with its children’s play area, terrain that runs from flatlands to hills, and a lake with hungry ducks--is their favorite picnic spot.

“It’s big, clean, the grass is always mowed, and there are lots of rides for the kids,” said Debbie Doody of San Pedro.

But it’s not the only park they go to for a picnic.

Elynor Olivadoti of Manhattan Beach said they also like Sand Dune Park. “It has a huge dune, like a four-story building,” she said. “You run up and down it.”

Enza De Cenzo of Manhattan Beach said picnicking in the park is a good way to meet other mothers and gives youngsters a chance to play with other children.

For thousands of South Bay people, picnicking--both the blanket-on-the-grass and table-top varieties--is as much a part of summer as traffic jams at the beach.

It’s free, although some parks charge for large groups that want reservations. And parks frequently have grills for cooking, ball diamonds, tennis courts, children’s play apparatus or swimming pools to provide an added attraction to picnickers.

Some picnic sites have special things that set them apart.

In Rancho Palos Verdes, Hesse Park has rolling land and ocean views. “We get a big crowd if the weather’s nice,” said park Director Nancie Silver. “There are a lot of birthday parties, mostly on weekends, and a lot of mothers bring their children here during the week.”

San Pedro’s Peck Park draws people whose tastes run to the rustic. “It’s large, kind of spread out, and there’s a canyon for hiking,” said Director Gary Shaughnessy.

A popular picnic spot in Carson is Scott Park, where Director James Foisia says people combine picnicking with swimming in the pool--one of only two park pools in Carson. Horseshoe pits--”we’re the only park that has them”--and a gym provide added attractions.

“We mainly get families and lots of birthday parties,” he said.

The Memorial Center is Hawthorne’s most popular picnicking spot, according to city parks and recreation Director Bob Klein. “We host a lot of families because we’re in such an ethnically diverse area,” he said. “Many Mexican citizens have birthday parties with pinatas. “

A picnic shelter, with gas cooking stoves, may be reserved by groups. Memorial has courts for basketball, handball and tennis, but Klein said people are free to organize their own softball games or put up nets for volleyball.

“We don’t restrict games, but we hope they don’t kill each other in the process,” Klein said. “It’s hard to have volleyball players competing where someone is trying to hit a softball.”

At Centinela Park, a 55-acre slice of the great outdoors in Inglewood, picnicking is a big operation--from a handful of friends to groups of several hundred that rent the park’s picnic arbors.

“We go through 5,000 picnickers a summer,” said Tom Barham, Centinela Park supervisor. “We’re the most popular park in Inglewood for picnicking.”

Tennis, swimming and softball are some of the park’s attractions, along with a rolling terrain dotted with firs and eucalyptus trees that give Centinela Park a back-to-nature feeling.

If South Bay parks get mostly family picnickers on weekends, they get people dressed in business attire during the week. These are the brown-baggers--called that even if their food comes in takeout containers--enjoying the outdoors on their lunch hours.

One man at Polliwog, in dress shirt and tie, was pitching golf balls. Some workers fed the ducks with leftover bits of their lunch.

“We’re here for the fresh air,” said Jina Cutler of San Pedro, who was having lunch at a picnic table with fellow TRW employee Cindy Matousek. They could see the top of the building they work in a mile away in Redondo Beach.

“We don’t have any windows where we work,” Cutler said, “and we heard it was the first day of summer, so we thought we’d better see what it’s like.”