When Rain, Rain Won’t Go Away, Improvise! : * Recreation: Junk mail, activity books and homemade clay may help children burn off excess energy while stuck indoors.

Sure, Southern California needs every drop of rain it gets.

But when gray skies and wet weather go on day after day, parents may find themselves at the mercy of children who have turned into crazed, cabin-fevered barbarians with energy to burn.

What’s a parent to do? OK, besides run away from home. There are ways to survive the great indoors with kids--and their relatively short attention spans--even when the weather outdoors stinks. Here’s how:

* Even in Los Angeles, you can save for a rainy day--by saving junk mail. Kids just love to open it, and because it’s packed with colorful pictures, stickers and boxes to check off, this is the perfect thing to keep them busy. Older children can even practice writing their name, address and phone number on the order forms.

(A word to the wise: Make sure none of the junk mail gets mailed, or it could multiply.)

* Stock up on books on children’s activities like water-based painting, connect the dots, paper-doll cutouts and coloring. Best of all, they require minimal cleanup.

* Stash a few boxes of cookie, muffin or brownie mix in the cupboard. Children love mixing, measuring and breaking eggs--and your house will smell great.

* Arts and crafts are a rainy day shoo-in, but remember, you need to plan--unless you always have construction paper and food coloring on hand.

* Homemade creative clay is a time-honored favorite. Children enjoy kneading and creating with it, and cooking it can be fun too. Mix:

1 cup cornstarch

2 cups baking soda

1 1/4 cup cold water

Add a few drops of food coloring, if desired.

Cook over medium heat about four minutes, stirring constantly until the mixture reaches a moist, mashed potato consistency.

Cover with a damp cloth until cool. Knead dough to create sculptures, ornaments, earrings and other designs. Let dry overnight, then paint with tempera or watercolor paints. Brush on clear shellac, clear nail polish or spray-on clear plastic.

* Kids love rubber stamps, but store-bought ones can be expensive. Potato-stamp art is an easy alternative that allows an infinite number of designs, as long as you don’t run out of spuds.

To make: Cut a small raw potato in half. Use a paring knife to cut shapes or designs into the open end. Color the designs with markers or use a stamp pad.

Let kids stamp butcher paper or paper bags that can later be used for wrapping gifts.

* Start saving throwaways such as paper-towel tubes, plastic foam meat trays, plastic soap bottles, plastic soda can holders, buttons and feathers. Add glitter, grains, dried macaroni, wooden beads and plastic eyes and you have the makings of ecology art.

* Action-oriented activities can be as easy as lining up chairs for a makeshift locomotive or having a living room floor picnic lunch. If you’re lucky enough to have a fireplace, try an indoor weenie roast using straightened coat hangers as skewers.

* Put on music and do some good old-fashioned exercises. Never mind that sit-ups, pushups and jumping jacks are not being executed with Jack LaLanne precision. Kids love to imitate adults, and a good 30 minutes of calisthenics will make everyone feel better.

* Try the latest dance steps and lip-sync the latest tunes, telling your young ones to pretend they’re Hammer, Michael Jackson, Paula Abdul or Mikhail Baryshnikov. Babies are especially fond of dancing cheek to cheek.

* Let the children do their best Sherlock Holmes. Give them a magnifying glass and a list of things to find around the house. Have them explain where they found each item.

* Take your children on a trip down memory lane. Bring out the old photo albums and home movies. Kids love to look at pictures of themselves and see the things they did as babies. If you’ve neglected to keep up the family photo album, this is a perfect time to catch up.

* Abandon the idea of keeping your home neat; it’s not going to happen. Make cleaning up at the end of the day a family project.

* Hope for sun tomorrow.