The rising cost of health care will cause a striking increase in the number of working Americans who probably won’ t be prepared financially to retire, according to recent findings by the Center for Retirement Research at Boston College.

CRR’s National Retirement Risk Index projects that 61% of workers today will be at risk of being financially unprepared to retire. That is a 17% increase from July 2007, when the Index number was 44%.

The findings offer a reason to be concerned but not to lose hope, suggests Paul Ballew, senior vice president of customer insights and analytics for Nationwide Financial Services Inc., Columbus, Ohio, which sponsored the Boston College study.

For one thing, Ballew said, most Americans need to change their savings and spending habits. “The personal savings rate in the U.S. today is essentially zero,” he said.

The Index means that 61% of households are not on track to maintain their preretirement, non-health-care level of consumption in retirement.

“The Index also shows that risk will rise for younger workers and low-income households,” says Alicia H. Munnell, CRR director. “The number could be considerably higher once long term care costs are taken into account, and if households do not plan rationally.”