The largest U.S. companies, including AT&T ( T), Best Buy ( BBY) and Exelon ( EXC), took part in a study that revealed a big disparity among racial and ethnic groups in retirement savings.

The report by Hewitt Associates ( HEW) and the Ariel Education Initiative, a nonprofit affiliate of Ariel Investments, showed that black and Hispanic workers participate and contribute less to 401(k) plans than whites and Asians do.

Hewitt and Ariel compiled information from nearly 3 million employees at 57 large -- primarily Fortune 500 -- companies, and took into account age, salary and job tenure. McDonald's ( MCD), Yum! Brands ( YUM) and Verizon ( VZ) also contributed data.

Sixty-six percent of black workers and 65% of Hispanics participate in their companies' defined-contribution plans, compared with 77% for whites and 76% for Asians. Blacks and Hispanics are also "more likely to have a loan and/or take a hardship withdrawal," the study said. As a result, "the 401(k) account balances for these workers are negatively impacted and chances for a comfortable retirement significantly compromised."

According to the research data, white employees contributed 7.9% of their income, higher than blacks and Hispanics, who set aside 6.3% and 6%, respectively. At 9.4%, Asian workers had the highest rate. The disparity exists even at higher pay levels. Black employees who earn $120,000 or more have saved, on average, $154,902 in their 401(k) plans, compared with $223,408 for their white peers.

Blacks are twice as likely to take a hardship withdrawal from 401(k) plans. Nearly two of every five and almost a third of Hispanic workers borrowed from their retirement accounts compared with one in five for whites.

"There is not really a single answer," said Barbara Hogg, a principal at Hewitt Associates and co-leader of the study. "It is important to point out that all groups are not doing great. We are behind on savings no matter how we look at it."

Savings goals and priorities may differ among cultures, Hogg said.

The promotion of retirement plans, from marketing materials to media coverage, seems to have a distinct Anglo-Saxon tint, she said.

"How are we making this a compelling story for people?" Hogg asked. "How do we draw them into the fact that they need to save for their future? When someone is talking about planning for retirement, the first words out of their mouth may be to 'save to the max,' a noble idea, but one not all demographics can afford to do."

Automatic enrollment plans and financial education as a mandated component of school curricula may help narrow the gap, the study said.