When a married couple buys a house or opens a savings account, they generally put it in joint names. They may also put joint names on mutual funds, stocks and other investments. If you buy a piece of property, the bank or real estate broker may insist on joint names (even though they have no right to do so).

Yet you may hear, or read, that joint ownership is a mistake. Lawyers say that it leads to tax problems and may complicate things when property has to be sold. In community property states, joint names conflict with state ownership laws, but are used all the same.

What's best for you? Do the objections of tax lawyers really apply to your situation? Here are the facts:

Joint ownership means a lot to married couples, especially to a wife who has no property of her own or doesn't work outside the home. It's tangible proof that marriage is a partnership and her contribution is valued. It gives her protection, because neither owner can sell the property or borrow against it without permission from the other. In case of divorce, the woman who has an interest in the property is in a better bargaining position than the woman who has nothing.

This same recognition can be given by putting property directly into the wife's name, including even a half-interest in the house. But it's simpler to use joint property. (In community property states, the law already decrees that one-half the property of the marriage is (hers.)

Another good thing about joint property is that when one owner dies, the property automatically passes to the other. There's no chance for delay while the will is being probated.

Some people even use joint property as a substitute for a will - not a good idea. If both of you died in an accident, the property would be divided according to your state laws, which might leave you favorite relatives out. In community property states joint property is generally treated as community property at death. To dispose of it the way you want to, you'll still need a will.

For people of modest means, the convenience and fairness of joint property generally makes it a good idea. (An exception is making joint investments. If both names are on a mutual-fund certificate and one owner is too sick, or too angry, to sign a sale order, the investment would be tie up. Stocks and bonds are best owned individually.)

But if the combined worth of husband and wife is more than $175,000, having property in joint names can raise your federal estate taxes dramatically.

Under the tax reform law, you can pass property tax-free to your spouse two ways - through the marital deduction (worth up to $250,000) and the credit against estate taxes (worth $175,000 by 1981). If you own all the property jointly, you're compelled to take the marital deduction and let the state-tax credit go unused. When the other spouse dies, he or she will be taxed on the amount of property over $175,000.

But if you own the property separately, you could set up a trust to shelter up to $175,000 with the estate-tax credit, and use the marital deduction on top of that, says Richard Covey, of the New York law firm, Carter, Ledyard & Milburn. That way as much as $425,000 may pass tax free. Furthermore, when the other spouse dies, the value of the trust will not be subject to tax in his or her estate.

But to do this, the property has to be owned separately, not jointly. And it ought to be divided between the spauses, so that each can take advantage of the estate-tax credit by setting up a trust. The potential estate-tax savings are really enormous - as much as $47,000.