A mother discovers the comfort of companionship

It had been one of ''those'' days. An unhappy preschooler attached to my leg, an ominous thump-thump in the washing machine, a child who spilled an entire gallon of milk (and later confessed that he had lost his brand-new jacket). Frustrated and lonely, I phoned a friend.

She listened with warmth and understanding, then shared her own challenges. The result? Two happier mothers. In listening to and reassuring each other, we had received the comfort we needed - and renewed strength.

Looking back to the days of overflowing diaper pails and endless toddler demands, I'm convinced I managed (and even enjoyed some of it), partly because I was surrounded by a group of other young mothers. Whether at our weekly bridge group (where we talked the evening away and played very few hands); during school volunteer activities; or even, sometimes, on a playground bench, there was always the opportunity to compare child-raising notes and to discover that I was not alone on this perplexing maternal journey.

I suspect it's different for the current crop of young mothers. Because of our increasingly mobile society, couples now often find themselves transferred far away from the old neighborhood where relatives and school pals still reside. The dropping birthrate and the rise in the number of employed mothers can further add to a sense of isolation for the young woman who remains at home. Where can she find others to reassure her that her two-year-old is perfectly normal (''Mine did the very same thing!'') and that shem is normal (''I don't blame you for feeling that way'') - or just someone to share the laughter and warm companionship that enrich the human spirit?

If you're a mother with a toddler hanging on your legs and a baby tossed over your shoulder, your free time is definitely limited. But if you make companionship a priority and weekly set aside some time to mingle with others, you're sure to stumble across a soul mate or two at:

* Evening adult education classes. These are the noncredit courses, usually offered by your school district, in everything from macrame to auto maintenance to conversational French. Choose something you've always wanted to learn. You may also discover a new friend sitting right next to you.

* Preschool programs. If you're feeling isolated, maybe your child is, too. Sign him or her up for a park, library, or preschool program - and try to volunteer some time occasionally. You'll meet other mothers with whom you can exchange child care, enjoy lunch, or share car pooling. One or two may turn into a ''forever'' friend.

* Church groups and civic groups.

Real and lasting friendships require an investment of time and need to be explored through many tentative conversations, as each person learns to trust the other. But the effort is well worth it. Not only do friends assuage the isolation of being at home, they also help us to become better mothers. Knowing that a warm and supportive peer group is standing by may be all that's needed to turn one of ''those'' days into a positive experience for everyone.