I'm in my early thirties, living with the man I plan to marry this summer. He is 12 years older, has been divorced for 10 years, has three children, 16, 13 and 10, and a bitter ex-wife.

They live in another state and we only see the children during the summer and at Christmas. We keep in touch with weekly telephone visits and letters.

I've only known the kids for a year, and for one extended visit. The kids are wonderful, and I think we're growing closer, but some things bother me.

The 13-year-old boy is great -- wise beyond his years and endearing -- and the 10-year-old is sweet, if somewhat moody, but the eldest boy is the worst. He's extremely intelligent (and lets everyone know it) and somewhat bratty. I don't think he'd help at all if he didn't have to.

I try to remember that they are just kids, but their mother doesn't make them keep themselves and their things neat and orderly. This is an ordeal for me, since I am rather compulsive about this. My fiance helps clean the apartment and cook, but they do a poor job when they clean and almost always break or chip something.

Money is a problem, too. They are given a fair amount when they arrive and told to save it for movies, eating out with friends, etc., but are constantly after us for more. We don't have much ourselves, and it's quite a strain just to feed the five of us. I find myself getting upset when their father doles out more. I think he does it because he feels guilty.

I think we should make a job chart when they visit this summer and give them a weekly allowance. If they don't keep their end of the bargain, we won't pay in full at the end of the week.

Please help me start this marriage on the right foot.

Right now you're on the left foot and it's hobbled at that.

It's time to rearrange your thinking so clashes with these children don't get worse, not just for their sakes but for yours. A tense relationship with your stepchildren will tear their father apart, and give the children a power over your marriage that will make all of you uncomfortable.

There's no reason to blame their sloppy ways on their mother, because you're sure to let it show and they will instinctively defend her by being even sloppier.

The truth is, most children are pretty messy between 10 and 16, especially when they're trying to squeeze their things into an apartment, without closets and bureaus of their own. Don't fuss about it. Just enlist one of the children to help you sort all the misplaced possessions -- clean clothes or dirty, rackets or jackets -- into three bags every day and leave them in a corner. The deal is this: A child can take something out of his bag, but only if he puts everything else away.

Tell them with a smile, though, and poke fun at yourself for needing to have things tidy. Children are much more cooperative when you blame yourself for an eccentricity, rather than blame them for a fault.

They should also make their beds in the morning, and help you clean the place at the end of the day, but do it in 15 minutes. This should be long enough for five people to scramble around picking up the papers, sodas and tapes and to blitz the bathroom and kitchen. And if you can't get it done before the timer rings? Thank them for their help and live with the rest of the mess, without making an issue out of it. People really are more important than appearances.

Their spending money shouldn't depend on the quality of their work, their dad shouldn't dole out extra money either, or they won't learn how to handle what they have. Ask him instead to tell the children what he can afford to give them for their whole visit -- according to their ages -- and then to give them a portion of it each day, since they seem to have trouble prorating it themselves.

Children need more than money to feel at home, however. They need to feel needed. Give them some simple, interesting recipes to cook, like a stuffed chicken or a lemon mousse, and plenty of compliments afterward. Praise is the balm of the soul.

Your interest in them is vital too, and you'll show it best if you ask them what they think about life, and how they plan to run the world. Children have big ideas, and they deserve to be heard.

They also need to see their dad more often. Encourage him to visit them whenever he can, or to invite one child at a time for one short trip a year, in addition to the regular visits, so you can get to know the individual child better.

You also should include the children in your wedding, perhaps with the five-minute service designed to reinforce the importance of any previous children in a new family. After you exchange rings, you and your husband would formally promise to care for his children. Questions may be sent to P.O. Box 15310, Washington, D.C. 20003.