As President Bush and Congress debate the future of Social Security, last year saw only a slight improvement in employees’ 401(k) participation rates, plan balances and diversification efforts, according to a new study by Hewitt Associates.

Compared with results from 2002, when Hewitt conducted its previous study, the participation rate in 401(k) plans increased slightly, to 70.3 percent — but for workers under the age of 30, that figure was just 46 percent.

The average 401(k) balance is now $69,000, according to Hewitt, but among younger participants — who will shoulder a great deal of retirement risk if the government creates private accounts for Social Security — 23 percent have a balance under $5,000.

Hewitt’s study examined the saving and investment behavior of more than 2.5 million employees eligible for their company’s 401(k) plan.

“Despite all the attention around retirement, it’s discouraging to see that many people — especially younger workers — still do not feel a sense of urgency to take control of their financial security by investing proactively in their 401(k) plans,” said Lori Lucas, director of participant research at Hewitt Associates, in a press release.

One encouraging finding: Fully 78 percent of employees who were contributing to their 401(k) plan last year set aside enough money to receive matching funds from their company. Even so, 31 percent contributed only enough to obtain the full company match, but no more. “Even those who contribute enough to obtain the full company match may only be contributing 3 to 4 percent of pay — a common match threshold,” observed Lucas. “This may be far too low to ensure financial security.”

According to Hewitt, the average 401(k) participant is 43 years old, has approximately 10 years of tenure, and earns an annual salary of approximately $58,000. The average nonparticipant is 39, has a little more than 5 years’ tenure, and earns about $33,000 per year.