With that in mind, it's time to answer those questions, and then some, now, before investors get worried about missing out on something that might help them.

        Officially speaking, the Roth 401(k) plan -- Roth-k for short -- was created in legislation back in 2001, but it actually becomes a tangible investment vehicle on Jan. 1. As the name suggests, the Roth 401(k) combines the features of a Roth individual retirement account with some of the attributes of a traditional 401(k) plan. Employers can offer the new accounts in addition to their current plan; investors would be allowed to contribute to one, the other or both.

Which brings us back to the first question: Will they or won't they?

        In this case, employers are the "they" and there is reasonable doubt that they will jump wholeheartedly into the Roth-k world. For starters, the Roth-k adds a new level of accounting complexity for the employer, and someone is going to have to pay for the servicing aspects of it. Few employers are volunteering these days to take on additional costs. See story of employers' Roth 401(k) plans.

        Moreover, employers are a bit concerned that the Roth-k will disappear after 2010, as it is part of legislation that has not been approved beyond that time (like the repeal of the estate tax and most provisions of the tax bill of 2001).

        Earlier this year, a Hewitt Associates study showed that 35% of large companies would consider adding the new type of 401(k). But might is hardly a sure thing.

Merits of the Roth 401(k)

        Contributions to a Roth-k are made with after-tax dollars, so they don't initially reduce a worker's tax bill. The money in the account grows tax-free and all withdrawals after age 59 1/2 are tax-free. In these respects, the Roth-k is like a Roth IRA.

        A regular 401(k) involves pretax contributions; the money isn't taxed while it stays in the account, but every penny is taxed as ordinary income when withdrawal time rolls around.

        In short, the regular 401(k) gives a tax break on the front end, while the Roth-k gives it to you on the back end.

        For anyone whose employer takes the plunge and offers the Roth-k -- and you can expect mostly large employers for at least the first half of next year -- which type of retirement-savings plan offers the bigger break will depend on the length of time the money is in the account, how much it earns and the worker's tax rate when putting the money in or taking it out.

Which brings us back to the second question: Should I or shouldn't I?

        If your employer offers a Roth-k -- and educational and non-profit institutions offering 403(b) plans will be able to add the Roth-k, but government employers currently offering 457 plans will not -- you'll be able to contribute to one, or both accounts. But you can't switch money from one to the other after it has been deposited.

        You also can't double your contribution limit by kicking into both plans; the same contribution limits apply to either account, or both combined.

        Employer matching monies must go into a regular 401(k), even if the worker is directing all retirement savings to a Roth-k.

        Unlike the Roth IRA account, the Roth-k will not have income limits, meaning that it will be an appropriate choice for wealthier families that heretofore have not been able to take advantage of this form of tax-free growth.

Doing the math

        If your employer doesn't offer the Roth-k, pushing for it makes sense. Feeling like you are missing out on a chance to get rich does not.

        "The analysis I have done in terms of financial benefit is that it its pretty marginal for a lot of people," says Ted Benna, president of the 401(k) Association and the guy who developed the first-ever 401(k) plan. "It's not as easy a decision as some people are saying it is."

        That's because if you contribute to a Roth-k, you lose tax deductions now; moreover, if you need to hold aside some of your current investment dollars in order to pay the taxes due on your savings, you won't be depositing quite as much into the Roth-k.

        Notes David Wray, president of the Profit-Sharing/401k Council of America: It's not a clear-cut decision for everyone, and it's not easy to figure out what's best. If you are paying more now in taxes and, as a result, are saving less, that may not be the best thing.

        "That gives people a reason not to save, and that is not what the Roth 401(k) is supposed to be about."

        Most advisers who have examined the Roth-k believe it will be an attractive option for younger workers who expect to be in a higher tax bracket in the future, and who have a lot of time to invest.

        If your tax rate in retirement is likely to be lower than it is today, however, the traditional plan probably comes out on top. By deferring the taxes today, your income and growth are taxed at the lower rate you expect to face in the future.

For older workers, the results could be as varied as the circumstances.

        "Generally speaking, it should be a very good thing for most people," says Ed Slott, who publishes Ed Slott's IRA Advisor newsletter. "A lot of employers will take a wait-and-see attitude, but workers should be pushing for this now. It might not be right for everyone, but you want the choice, because that's when you do the math and can learn if this is really going to be a big help."