At a committee hearing Thursday on Americans saving for retirement, US Senator Elizabeth Warren asked a panel of experts, including a Fidelity Investments executive, what could be done to encourage more employers to offer 401(k) and other plans.

“On the one hand we could require the employers to participate,’’ said Warren, a new member of the Senate Health, Education, Labor and Pensions Committee. Or, she asked, are there incentives that could encourage small businesses and others to offer their workers retirement plans.

Julia McCarthy , executive vice president for Boston-based Fidelity, said the time spent administering these plans, as well as the fiduciary responsibility that comes with them, stop many small employers from offering them.

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Also testifying was Brigitte C. Madrian, a professor of public policy at the Harvard Kennedy School in Cambridge who has researched retirement plans. She said that to encourage more companies to offer plans, “there need to be very simple options for employers, very minimal regulatory requirements,” as well as limited fiduciary requirements. She also suggested that Congress could provide a modest tax incentive for companies that offer 401(k)-type plans or matches.

The panelists said the recent adoption of plans that allow automatic enrollment of new employees in 401(k) plans has increased participation. Fidelity’s McCarthy said the partipation rate is 88 percent in plans with automatic enrollment, compared with 67 percent across all plans it manages.

But she also urged companies to enroll workers with higher contributions—at 6 percent instead of 3 percent for instance. In addition, she said, employers could make more generous matching contributions, to give workers incentives to save more.

Women in particular face challenges saving enough for their old age, according to testimony by Cindy Hounsell, president of the Women’s Institute for a Secure Retirement, a Washington-based advocacy group. Some are affected by losing their spouses, while many others struggle because they are caregivers or work in environments where there are no retirement plans available.

Said Senator Tom Harkin, the Iowa Democrat who chairs the committee, “Americans are terrified about whether they will have enough money to live on when they stop working.”