As space in houses and apartments shrinks, the value of designing with mirrors goes up. Mirroed surfaces always visually expand space, and they are used today in dozens of imaginative ways.

Two California interior designers have ideas that could be adapted to homes anywhere.

Jim Simpson of Palm Desert has found a dramatic way to use a mirrored end wall to double the illusion of space in a small dining room. The mirror panels also provide a dramatic frame for a wall cabinet painted in an abstaract design.

Designer Carole Eichen of Fullerton uses mirror panels as interior "windows" on solid walls, to reflect light and project pattern and color from one wall to another. In a long narrow kitchen, she as made a mirror "cafe" window with a checked awning over the top and glass shelving for showing off decorative mugs and pots.

Here are some things to remember when youy are experimenting with mirrors:

When you put up a mirror or mirrors, you add the quality of movement to your room through the decorative replay of light and shadow, shapes and others.

Mirrors have been used since the middle of the 18th century. They appear to double room sizes, and they increase light from wall brackets and chandeliers.

To widen a narrow room, mirror one of the long walls, or both of them.

Remember that floor-to-ceiling mirror strips can heighten a room visually. Such mirror strips are often combined these days with weathered barn wood or clear pine. Mirror stips may run verticaly, horizontally, diagonally, or be arranged in giant zigzag patterns.

You can hang a handsomely framed mirror on a mirrored wall with elegant effect. You can also hang a painting against a mirrored wall.

You can mirrors a ceiling if you so desire, but you must remember that it duplicates everything in the room, so you must judge if the quality is worth a double image. Many big-city decorators are now using more subtle black mirrors for ceilings and walls.

An accent framed mirror can look very good in a wall arrangement of paintings or prints.

A whole collection of framed mirrors in varying shapes and sizes can be as effective on a wall as a series of paintings.

A mirrored folding screen can add glamour to any room.

Framed mirrors can be used any place where there is something worth reflecting. They should not be linited just to places above the fireplace mantel or over the front hall console. Hang one, for instance, over the sideboard in the dinging room to reflect attractive foods.