Pinched by the economic downturn, many Americans have cut back on saving for retirement, especially younger workers, a recent Opinion Research survey found.

Sixty-three percent of 1,005 respondents polled said they've stopped contributing to their retirement plans. Additionally, just 54 percent said they're currently investing in a retirement plan, and only 21 percent said they have $50,000 or more in assets.

According to Diane Young, the director of retirement planning at TD AMERITRADE, the investment firm that commissioned the survey, scrimping on retirement savings is "not good practice."

"We find it very alarming," Young said. "The reality is, when the markets do come back as they always tend to do, we as Americans are still going to be faced with needing to be better prepared financially in retirement."

Half of respondents who stopped or reduced contributions said financial strain is affecting their ability to continue to save for retirement. Others cited unemployment and rising health-care costs.

More than any other group, respondents aged 35 to 44 indicated they have stopped or reduced their retirement plan contributions, the survey found.

Young said this age group needs to be more cautious by preparing for potential changes in Social Security availability.

"I think people who are 35 to 44 feel they have some time to recover if they need it, but the reality is they should be a little bit wiser, especially as they see what their parents are going through," Young said. "So they need to readdress their thinking on what it takes to save and the value of compounding."