WASHINGTON — Younger Americans in their late 30s are now the group most likely to doubt they will be financially secure after retirement, a major shift from three years ago when baby boomers nearing retirement age expressed the greatest worry.

The survey findings by the Pew Research Center, released Monday, reflect the impact of a weak economic recovery beginning in 2009 that has shown stock market gains while housing values remain decimated.

As a whole, retirement worries rose across all age groups — roughly 38 percent of U.S. adults say they are “not too” or “not at all” confident that they will have sufficiently sized financial nest eggs, according to the independent research group. That’s up from 25 percent in 2009.

But the concerns are increasing the greatest among younger adults approaching middle age, whose equity in their homes represents most of their net worth. About 49 percent of those ages 35-44 said they had little or no confidence that they will have enough money for retirement, more than double the 20 percent share in that age group who said so in 2009.

Baby boomers born between 1946 and 1964 also reported having more retirement anxieties than before, but now to a lesser degree compared to their younger counterparts. About 43 percent of Americans ages 45 to 54 expressed little or no trust in their retirement security, up from 33 percent in 2009. Among Americans ages 55 to 64, the share expressing little or no confidence was 39 percent, up from 26 percent.

Broken down by smaller groups, the Pew analysis found that retirement worries peaked among adults in their late 30s; a majority, or 53 percent, of Americans ages 36 to 40 lacked confidence that they will have large enough nest eggs. Just three years ago, it was baby boomers ages 51 to 55 who had the most anxiety over whether their income and assets would be sufficient.