Washington ? American workers, who face growing financial pressure to stay in the work force, are far more likely to be forced into an early retirement than many expect, according to a study released Monday.

Four out of 10 retired workers left their jobs sooner than they had planned, usually because of health problems or the loss of employment, according to the report by McKinsey & Co., which was based on a national survey of 3,086 people.

The survey also found that 45 percent of people who are currently employed planned to keep working past age 65. But among the retirees polled, only 13 percent said they had done so.

The findings raise fresh concerns about Americans’ ability to afford a comfortable retirement. With more companies abandoning or freezing their pensions, many people say they plan to work longer to build up their nest eggs.

The reality “is quite sobering,” said David Hunt, a senior partner at McKinsey. “Our research clearly shows that many people – and more than a few public policymakers – who are betting on simply working longer to compensate for a lack of current savings are setting themselves up for a rude awakening and a significantly poorer standard of living in retirement than they had expected.”

The McKinsey survey included retirees, for which it had a 3.2 percent margin of error, and people who are not retired, for which the margin of error was 2.4 percent. It was conducted in March and April among people 40 to 75 years old.

For many, there is no way to see a forced retirement coming.

“They get laid off. They have health issues that prevent them from working,” said Sandra Timmerman, director of the MetLife Mature Market Institute in Westport, Conn.

At the same time, Timmerman noted, workers face the need to maintain their careers to set aside money for retirement.

“I think we’re seeing the realization on the part of people that they ought to extend their work life longer than in the past,” she said.

It is a realization brought on by the changing landscape for retirement security. Many employers no longer provide traditional pensions with guaranteed monthly payments. Instead, they offer 401(k) savings plans, and it’s up to the workers to salt away enough money to last them in old age.

Just last week, Fidelity Investments reported that 83 percent of workers felt they were not saving enough for retirement, up from 78 percent last year.