During the summer, Washington cleared up a lot of uncertainty by making higher limits permanent. (Generally, the 401(k) rules also apply to 457 and 403(b) plans, which are similar retirement plans.)

There's no question this can be very valuable. The Investment Company Institute, the trade group for mutual fund companies, figures that with higher contributions made permanent, a 40-year-old who started an account in 2002 and contributed the maximum every year would have $304,000 by age 65. Had the higher contribution limits been allowed to expire after 2010, the account would grow to just $172,000.

The same investor starting a 401(k) in 2002 and contributing the maximum every year would have an account worth $1.1 million at 65. That compares with $888,000 if the higher contribution limits expired four years from now.

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That all looks good on paper. But in real life, very few workers contribute the maximum allowed, even under the lower limits of the past.

About a third of eligible employees contribute nothing to 401(k) accounts, according to a new study by Fidelity Investments, which manages these plans for about 12,000 companies with nine million eligible employees.

The average employee puts in only 6.9 percent of his salary, though many employers allow up to 20 percent. Nearly half of all 401(k) participants have accounts worth less than $20,000.

Yes, it's nice that you can put a bundle into an IRA or 401(k) - but in practice, many people can't afford to.

Or they don't realize how valuable these accounts are. To address that, Washington over the summer changed the rules to make it easier for employers to automatically enroll new workers in 401(k)s, starting in 2008. Previously, many states barred this, and proponents have touted this change as a big leap forward.

Although employees will have the right to opt out of the plans, various studies have shown that they tend not to. At companies that already have automatic enrollment, about 76 percent of eligible employees participate compared with 54 percent at companies without this feature, according to Fidelity.

During the summer, the Financial Economists Roundtable, composed of about 50 of the country's most prominent economists, put automatic enrollment at the top of its list of beneficial retirement-plan improvements.

"There wasn't much disagreement on that," said Marshall E. Blume, a Roundtable member who is a finance professor at the University of Pennsylvania's Wharton School. Automatic enrollment should lead to better 401(k) participation, which is critical as more and more companies use these plans to replace traditional pensions, he said.

Still, the Fidelity data show that even firms with automatic enrollment generally don't get employees to contribute the maximum.

Perhaps that will change under another new federal rule passed this summer, making it easier for employers to offer workers investment education. While many companies already do this, the advice tends to be generic. Now that employers are protected from lawsuits from workers who follow the advice, more companies are expected to add services tailored to individual workers.

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Taken together, the changes I've discussed, along with others on the accompanying list, are good. But their effects are likely to be modest.

"I have not heard anyone comment to the effect that it's made any difference in their way of investing at all," says Ginger Hoyt of Telford, president of the Delaware Valley chapter of the National Association of Investors Corp., an organization that teaches people to handle their own investments. It has 3,000 members in the Philadelphia region.

Advocates for small investors have long sought two changes that might really make a big difference - but Washington has so far declined to grant them.

One would defer taxes on investment gains, such as annual capital-gains distributions from mutual funds, if they were immediately reinvested. Money that otherwise would be used to pay annual taxes would thus be left in the accounts to compound longer, boosting returns.

The other would allow more people to use Roth IRAs, which offer the same tax-free withdrawals as Roth 401(k)s. Currently, only people with incomes below certain thresholds can contribute to these accounts, and no more than $4,000 can go into them in a single year (or $5,000 for people over 50).