Save the Earth--and Have Some Fun, Too : Holiday: The Fourth of July weekend offers some swell ways to show your appreciation for the environment, from planting a tree to beachcombing to touring a water-saving garden.

Did terms like biodiversity and global warming make you ignore Earth Day this year? Relax. You can easily participate in saving the environment and have fun doing it during the upcoming Fourth of July holiday.

Saving the Earth simply means celebrating and appreciating nature--something that happens anytime you picnic in a park, spend a day at the beach or lounge in your back yard.

But while we’re enjoying the great outdoors, ecologists want us to envision a park without litter, a beach without broken glass and a tree-shaded yard that doesn’t drink gallons of precious water.

These environmental trespasses may appear minor when compared to toxic waste, for example, but any pollution--no matter how small--contributes to the ill health of our planet.

Saving the Earth may seem like a monumental task, but each person can aid the healing process in simple and enjoyable ways. Here are a few ideas to get you started:

HOST A TREE-PLANTING PARTY: What’s a back yard without a great shade tree to nap under or a beautiful garden to admire? Both add to the “greening” of the Earth. First choose a tree and California native plants that are drought- and pollution-resistant. Just like an old-fashioned barn raising, invite family and friends to help with the planting and serve them an easy-to-prepare buffet and cold drinks. For planting and garden tips contact:

* TreePeople, 12601 Mulholland Drive, Beverly Hills, (818) 753-4600. The group that started the urban forest movement offers a list of trees suitable for Southern California.

* Theodore S. Payne Foundation, 10459 Tuxford St., Sun Valley, (818) 768-1802. Open Tuesday-Saturday 8:30 a.m.-4:30 p.m., the nursery has 600 species of California native plants, 100 of them rare and endangered. The bookstore has books on how to make your garden grow. For $2, you get three catalogues on seeds, plants and books.

TAKE A DRIVE: Go ahead. Feel good about taking the car for a Sunday drive, but bring the family with you and now you’re car-pooling. Pass up fast-food places and their throwaway containers and pack a fresh homemade lunch. Get your car tuned and your tires checked ahead of time and you’ll use gas efficiently.

GO ON A PICNIC: Shop for picnic supplies with a canvas tote and forgo so-called “biodegradeable” plastic bags that sit in landfills, or paper sacks that are rejected by many recyclers because of low market value. Buy a set of colorful reusable picnic ware and bring cloth napkins. For children, make a contest out of picking up litter. Provide small prizes or treats for their efforts. Good picnic spots:

* Placerita Canyon Nature Center, 19152 W. Placerita Canyon Road, Newhall, (805) 259-7721. Open daily 9 a.m.-5 p.m. Free. Picnic where gold was first discovered in California. Walk on the half-mile ecology trail and view park wildlife exhibits.

* South Coast Botanic Gardens, 26300 Crenshaw Blvd., Palos Verdes Peninsula, (213) 377-0468. Open daily 9 a.m.-5 p.m. Adults $3; seniors 62 and older/students with ID $1.50; ages 5-12, 75 cents, and under 5 free. These gardens thrive on a recycled landfill. Picnic tables are on the lawn area outside the grounds.

GO BEACHCOMBING: Bring a cooler of lemonade and comb the beach for trash. Bag all aluminum, plastic and glass containers for recycling. Snip any plastic six-pack rings because they maim and kill ocean animals. At beaches with rock outcroppings, find the tide pools and observe ( never touch or remove) some of the marine wildlife you’re protecting. Then spread out a towel, soak up the sun and remember the sunscreen and sun hat. For information on tide pools, contact your county department of parks and recreation.

HEAD FOR THE HILLS: Spend some time in the wilderness and get a sense of what saving the Earth is all about. National parks are ideal. Observe the motto: “Pack it in, pack it out.” Check with a ranger station or visitor center for wilderness tips, nature trail maps and park wildlife programs.

TOUR A GARDEN: Water-conserving gardens called xeriscapes--are not drab, cacti-laden landscapes. They contain a variety of colorful low-water-use flowers, flowering shrubs and ground covers. Daffodils, wisteria and sweet alyssum are just three of them. Take a tour and see how they might look in your back yard.

* Charles Lummis Garden, 200 E. Ave. 43, Highland Park, (213) 222-0546. Open Thursday-Sunday 1 p.m.-4 p.m. Free. A prime example of xeriscape adjacent to the historic Charles Lummis Home and Museum that houses the Southern California Historical Society.

VISIT A MUSEUM: Natural history museums and similar places are great sources of information about our environment. The following are concerned year-round with environmental education and preservation:

* Cabrillo Marine Museum, 3720 Stephen White Drive, San Pedro, (213) 548-7562. Open Tuesday-Friday noon-5 p.m.; Saturday-Sunday 10 a.m.-5 p.m. Free, but parking is $4.

* Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, (213) 744-3534. Open Tuesday-Saturday 10 a.m.-5 p.m. Adults $3; seniors/ages 12-17, $1.50; ages 5-12, 75 cents; under 5, free.

TAKE A CLASS: Learning about the environment doesn’t have to be a bore. You can take a class or attend a program given by ecology-minded groups and natural history museums.

* The Wilderness Institute, 28118 Agoura Road, Agoura Hills, (818) 991-7327. Classes include low-impact camping, fossil digging and paper-making. Free catalogue.

* California Native Plant Society, Santa Monica Mountains Chapter, 455 Almar Ave., Pacific Palisades, 90272, (213) 933-8993.