NEW YORK -- Starting next year, you may have access to a brand new 401(k) option aimed at decreasing your tax burden in retirement.

Deciding whether or not to contribute to the new option -- known as a Roth 401(k) -- however, may require some crystal-ball gazing. Highly paid workers are the most likely to take the gamble and contribute to this new type of account. They are also the most likely to see it pay off, tax experts said.

The Roth 401(k) combines elements of the traditional 401(k) with the tax benefits of the Roth IRA. It allows people to contribute to tax-deferred savings accounts with after-tax dollars in exchange for the benefit of withdrawing that money tax-free in retirement. The traditional 401(k) is funded with pre-tax dollars and withdrawals are taxed as income.

Currently, more than 30 percent of employers surveyed said they were very or somewhat likely to offer a Roth 401(k) next year, according to data from consulting firm Hewitt Associates Inc.

Workers with access to both a Roth and a traditional 401(k) will be limited to the same contribution cap as people with just one 401(k): a maximum of $15,000 for 2006, or $20,000 for people age 50 and over by the end of the year. This leaves workers with three choices: They can continue to contribute solely to the traditional 401(k); they can divert their contributions to the Roth 401(k); or they can split their contributions between the two accounts.

For workers to gauge whether the benefit of tax-free withdrawals down the road is worth the upfront cost, they will have to predict their personal tax situation in retirement. As a general rule, the Roth is a good solution for people who expect to be in a higher tax bracket in retirement.

In addition, they must also take a stab at forecasting what the national tax picture might look like when they're ready to tap their nest egg. If tax rates rise to pay off the growing budget deficit, paying taxes now is a good deal. Of course, "you're kind of shooting at a moving target in trying to predict tax rates," said Richard O'Donnell, a pension expert at RIA, a Thomson Corp. unit that provides information and software to tax professionals.

Many tax professionals predict taxes are going to head higher to pay off the nation's financial debt. There is always the chance, however, that the government will dump the current tax system in exchange for a lower flat tax or a sales tax -- ideas that have been gaining traction in recent years, said Allen Buckley, a partner and employee-benefits lawyer with Smith Moore LLP in Atlanta. If this happens, people who have invested in the Roth 401(k) will "lose big time," he said.

One reason the Roth 401(k) is expected to be most attractive to high-income workers is that it will mark the first time they have access to a savings account that offers tax-free withdrawals in retirement. The only other savings account that currently offers that benefit, the Roth IRA, carries strict income stipulations. Roth IRA eligibility is off limits for single filers who earn more than $110,000 a year, and for joint filers who earn more than $160,000 a year. The Roth 401(k) carries no such restrictions -- anyone can invest in one so long as the employer provides this option.

Another reason high-income people are more likely to take the gamble is that their tax rates are currently quite low, based on historical data, which improves the chance that rates will be higher for this group come retirement. "It only makes sense that the government will increase tax rates for higher-net-worth people," said Barry R. Milberg, founder of Milberg Consulting, a provider of retirement and pension services in Blue Bell, Pa.

Also, the Roth 401(k) may present a unique estate-planning benefit for wealthier people, said Milberg. Since tax is paid on the money going into the Roth, there's generally no required minimum distribution age. With the traditional 401(k) or IRA, the government requires minimum distributions starting at age 70.5 to ensure people eventually pay some tax on the money.

Currently, there's a minimum distribution requirement on the Roth 401(k), but investors may be able to get around it by rolling their accounts into a Roth IRA, which doesn't have such requirements. That means people with a Roth IRA can delay taking distributions from the account, thus preserving what they can pass on to their heirs in a tax shelter. This can't be done as well with a traditional IRA because of the minimum distribution requirements. Plus, heirs who receive IRAs inherit the tax benefits of these accounts -- although they are required to make some minimum distributions through their lifetimes.

(Just a word of warning: This loophole could close before these accounts are made available next year, so people who are counting on this benefit want to keep an eye out for further IRS guidance on the topic.)

Workers who aren't sure what they should do could always contribute to both, hedging against the risk of both lower and higher taxes in retirement. Of course, there isn't a lot of time for workers to ponder the issue. The Roth 401(k) -- which was created with the Economic Growth and Tax Relief Reconciliation Act of 2001 -- is set to expire in 2010, unless Congress takes steps to extend this benefit.