In the midst of the Christmas bustle, there is an unlikely question nagging many American workers: "What's all this hoopla about IRAs?"

Along with the toasters and the food processors, the holiday ads have begun to push something new in the often complex world of finance to help you combat inflation. Even if you don't keep up with business news, it would be hard to miss the IRA's sudden leap into the spotlight.

"Shouldn't I take a look at this?" you ask yourself, and then the thought slips from your mind as you pop another batch of sugar cookies into the oven. But, say Washington financial advisers, IRAs deserve as much of your attention as Santa -- and they almost certainly will be more rewarding than that stocking hung by the chimney with care.

As of Jan. 1, 1982, for the first time, every one of the estimated 107 million workers in this country is eligible to set up an IRA -- an Individual Retirement Account. For those under 40 -- with at least 30 working years ahead -- an IRA, say some ads, could provide a retirement nest egg of as much as a half-million dollars.

If, for example, you contributed the maximum allowed of $2,000 each year for 30 years at 12 percent interest compounded each year, estimates Nina Gross, counsel for the American Bankers Association, you could expect $540,585.20 ready and waiting when you retire. "That," she says, "is very, very nice."

For working couples, where both husband and wife sign up for an IRA, the family figure doubles to $1 million or more -- before taxes.

"You'll be a millionaire only for a short time," notes Peter Elinsky, a tax partner in the in the Washington office of the accounting firm of Peat Marwick Mitchell and Co. And there is no assurance your money will consistently earn at 12 percent or that a half-million bucks will buy what it does today. Nevertheless, he considers IRAs an "excellent" investment.

IRAs are "a very, very big thing," says Reg Green, vice president of Investment Company Institute, an association representing 90 percent of the nation's 600 mutual funds, who are looking for a major share of IRA accounts. "We calculate $20 billion will be invested in each of the next few years."

"Every client we have is being contacted," says financial consultant Kathleen P. Lander of Lander Associates, who teaches a personal financial planning course at Mount Vernon College. "We are now accumulating checks and applications." For people who are not severely pinched for cash, an IRA "is the best tax shelter an individual can buy."

"Our phones are ringing off the hook," says Doug Rogers at Perpetual American Federal Savings.

"There is fantastic interest in them," says account-executive William Kirvan of Merrill Lynch Pierce Fenner and Smith.

Under a new tax law passed this year, each worker can establish his or her own retirement plan and contribute up to $2,000 annually. For working couples, each may pay in $2,000. If one spouse has no income, a spousal account can be established, with a total family contribution of $2,250 yearly (divided between wife and husband in separate accounts as they see fit).

Among the benefits making IRA so popular:

* The amount invested each year can be deducted from your income tax. For example, says the Investment Company Institute: "If you're in the 33 percent tax bracket and put away $2,000 a year . . . you'll save $660 in taxes immediately." The higher your tax bracket, the more you'll save each year you invest.

* The interest, dividends and capital gains the investment earns are not taxed immediately. That means the same amount of money invested in an IRA will grow more rapidly than non-IRA investments, which are subject to taxes. By the institute's calculations:

"Let's say you're in the 33 percent tax bracket and invest $2,000 annually in a regular investment that returns, on average, 10 percent yearly. At the end of 20 years, the value of your investment would be $84,372." In an IRA, under the same conditions, the amount is $126,005, "because you didn't pay taxes on the earnings . . . "

(You eventually do pay taxes on your IRA investment and earnings, but only as you withdraw them. The earliest you can take them out without penalty is age 59 1/2 -- or if you become disabled -- though you may want to wait until you actually retire. They are then taxed as ordinary income. Presumably, retirement will have dropped you to a lower tax bracket, reducing the taxes you owe. You must begin to withdraw funds by age 70 1/2.)

* The job-hopper who doesn't remain long enough to collect pension benefits can continue to build a retirement fund wherever he or she is employed. Or, if you quit a job and are eligible for a lump-sum payment of retirement benefits, the money can be put into a tax-deferred IRA account.

* With Social Security shaky and employer-funded retirement plans often inadequate, you are systematically providing a supplemental source of funds to see you through possibly 30 years of retirement.

Nevertheless, IRAs are not for everyone, warn financial advisers. If you do invest in such a program, plan on seeing it through until you reach 59 1/2 because the penalty for early withdrawal is severe.

"I see a lot of people coming in on Jan. 4" to invest, says Glenn Schickler, vice president of Madison National Bank, "then in July saying, 'I've got $700 here I could use for something else. I lost my job or I'm going on vacation.'

"An IRA is not a substitute for saving for an emergency in the family. This is not a savings program for short-term goals."

To get back the $700, he says, you would be nailed with a 10 percent penalty ($70, in this case) to the government plus regular income tax. Additionally, if you've invested in something like an 18-month certificate of deposit, you could lose six months' interest.

Adds Merrill Lynch's Kirvan: "Liquidity is important. You've got to be careful. People at a party may be saying, 'You'd be a fool without an IRA.' But I've got a kid going to college. I'd be a fool to take out an IRA. I need every penny."

As with any investment, says the institute, "You should think carefully before committing your money."

IRA's are being offered in a variety of forms by banks, savings and loan offices, credit unions, stockbrokers, mutual funds, insurance companies and employers' payroll deductions. The plans differ in degrees of risk, administrative fees and other charges, flexibility, the rate of return and the minimum amount you must invest to get started (some will accept as little as $25 a month).

To determine what suits you and your goals best may take some shopping around. Once you've chosen a plan, you are not committed until you retire, but can switch to another option at least once a year without penalty.

Nor is it necessary to jump into an IRA immediately. To get the tax deduction for 1982, you can invest anytime up until you file your tax return before April 15, 1983. Advises the institute: "If you invest late in the year, you have the advantage of being able to determine more clearly how much you can afford to invest." Those who do sign up right way, however, begin accumulating tax-deferred earnings for the maximum benefit.

There is no requirement that you must contribute the full $2,000 annually -- that's the maximum. And in lean years, if you choose, you can skip the contribution altogether. You can even split the $2,000 between different investments.

The institute's Reg Green expects that about 20 to 25 percent of American workers in the $20,000 to $50,000 income range will sign up for some form of IRA in the next couple of years. Maybe as many as half of those who make over $50,000 will do so. As for the rest in the middle-income brackets:

"Lethargy," he suggests. "We all know we should be doing something that we aren't."

For more information:

IRS publication 590, "Individual Retirement Accounts," expected to be available in IRS offices by next week. Pamphlet order blanks will be mailed out with this year's tax forms.

Among free pamphlets available by mail:

* "Plan Tomorrow Today With Your Own IRA," (along with a pitch for mutual funds). Investment Company Institute, 1775 K St. NW, Washington, D.C. 20006, Attn: IRA Dept.

* "What You Should Know About Annuities." American Council of Life Insurance, 1850 K Street NW, Washington, D.C. 20006. CAPTION: Illustration, no caption, By Halley Mason -- The Washington Post; Table, Future Value of Annual Investments of $2,000, Courtesy, Investment Company Institute