If you're married, you probably imagine that you and your spouse both own property you've collected over the years, with the survivor to inherit everything. If you plan to marry, you may assume that shared ownership will be part of the deal.

But you're equal owners of marital property only in the eight community-property states (Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington), or if you hold your property in joint ownership. Otherwise, the property belongs to the spouse whose name is on it. If the man holds the brokerage account, he normally owns all the stocks--even if some of the money he's investing is his wife's. If the woman holds the savings account, it's hers, even if she uses the money for family purposes.

In the day-to-day business of running a marriage, who owns what doesn't matter very much. But at death or divorce, the spouse whose name is not on the property could wind up with the short end of the stick.

It's unfair that spouses should have to have their papers in order, to assure each partner gets a fair share. In this respect, the community-property states are right: Shared property ownership should be built right into the laws of marriage.

In pursuit of that truth, the National Commission On Uniform State Laws has just approved a new Uniform Marital Property Act, which it will try to persuade the states to adopt. In the eight community-property states, UPMA would mainly cause cosmetic changes in procedure. But in the other 42 states, it would bring the security of ownership to spouses who otherwise might have no legal stake in the property of their own marriages. For example:

* At death, in many states, three things can now happen to unfairly cut out a spouse: might inherit no more than one-third of the property, if the other died without a will. (2) The deceased might have evaded the law that makes it illegal to disinherit a spouse. For example, a husband might hold all his property with his girlfriend in joint ownership; it would then pass to her, even if the spouse was left with very little money. (3) If the husband holds everything in his name, and the wife dies first, the wife can't leave any property to another person. For example, she might not be able to leave anything to her children by a previous marriage. In this instance, she has no access to the marital property that she had a stake in creating.

UMPA would change all that. At death, the surviving spouse would automatically own half the marital property, including property that the other spouse might hold jointly with someone else. Whichever spouse died first would have the right to leave up to half of the marital property to someone else, by will.

* At divorce, a couple can agree to divide the property in any way they choose. But if they can't agree, courts in three states will award the property to the spouse whose name is on it; courts in four states may require that the property be divided 50-50. The remaining states allow for "equitable distribution," which means that the court can split the property in any manner that seems fair.

Under equitable distribution, it shouldn't matter which spouse formally owns the property. In practice, it matters very much. "It's the psychology of it," says William Cantwell, Denver attorney and author of the UMPA. "If the husband has the investments in his name and a court tells him to give half to his wife, he'll think he's been taken to the cleaners. He resents being divested of his property, and may make it hard for his wife to collect. But if the couple knows right from the start of the marriage that half of the property belongs to each, they're more comfortable about making a fair distribution."

A husband and wife can agree to change the 50-50 ownership presumed by the Uniform Marital Property Act--so they're not locked into shared property if they don't want it. They can hold as separate property anything they brought into the marriage, or any inheritances. The person whose name is on the property still has full rights to manage it.

But despite the good in the proposed law, states may not rush to adopt it. There's plenty of opposition--from lawyers who mistrust any change in forms of ownership, and from male legislators who just plain don't want to give their wives an ownership right in what they earn.

A bill similar to UMPA almost passed the Wisconsin Legislature last year and has a good chance of passage this year. But it will take the zealous backing of women's groups in many states to make property sharing in marriage the law of the land.