The new Individual Retirement Accounts, on sale after Jan. 1, are a wonderful windfall tax shelter for most Americans. If you never managed to save money before, it is worth the effort to save it now. Here are some answers to the many questions that I am already getting in the mail about IRAs:

* Do I have to do anything about the new IRAs right away?

No, you do not. You have plenty of time to learn more about them and decide what you ought to do. Money deposited in a new IRA will be deductible on your 1982 income tax return, which you do not file until 1983. The sooner you start on an IRA, however, the faster you will start earning interest on your savings, tax-deferred.

* How is the new IRA different from the old one?

Many more people will be eligible to start IRAs than could start them in the past. Also, the maximum contribution has been increased.

When you put money into an IRA, it is deductible on your income-tax return. For example, if you have a taxable income of $30,000 and contribute $2,000 to an IRA, you will be taxed currently on only $28,000 worth of income, for a current tax saving on a joint return of $638.

Any interest, dividends or capital gains earned on your IRA savings are allowed to accumulate, tax-deferred. But don't forget that these are long-term savings. If you take any money out of an IRA before age 59 1/2 (except in cases of death or disability), you incur a 10 percent tax penalty. All money withdrawn from an IRA is taxed as ordinary income.

* I already have an IRA. May I start using the new rules right away?

No, you may not. It is very important for present IRA holders to distinguish between what can be done for their 1981 tax returns and what has to wait until 1982.

You are eligible for a 1981 IRA if you work for a company that has no pension plan, or if your company does not cover you with the plan it has. Under this year's rules, you may contribute up to 15 percent of your earnings or $1,500, whichever is less. If your IRA includes a nonworking spouse, your maximum contribution rises to $1,750.

Anyone eligible for a 1981 IRA should certainly take advantage of it. You may start the IRA and make a tax-deductible contribution all the way up to the due date of your 1981 tax return, which is April 15, 1982 (or later, if you get an extension).

The brand-new IRA rules take effect on Jan. 1, 1982. Contributions may begin right away. Some people will be making their 1981 and 1982 IRA contributions at the same time. But your 1982 contribution will not be deductible until your tax return in 1983.

* What are the new 1982 rules?

Starting in January, anyone with earnings will be allowed to have an Individual Retirement Account. You may start an IRA even if you already maintain a company pension plan or a Keogh Plan.

You may put up to $2,000 a year into the IRA regardless of earnings (with this exception: if you make less than $2,000, you may contribute no more than 100 percent of earnings). If your IRA covers a nonworking spouse, your maximum contribution rises to $2,250.

* May I contribute to an IRA and a Keogh Plan in the same year?

Yes, you may. In fact, if you work for a company that requires you to contribute to your pension plan, and you keep a Keogh Plan for your income from moonlighting, and you start an IRA, you may sock away tax-deferred savings in all three.

* May I start an IRA even if I don't work?

No, you may not. IRA contributions may be made only by people with earnings. You cannot fund an IRA if you receive income only from such sources as interest, dividends and rents.