NEW YORK – Americans 45 and older are far more open to sex outside of marriage than they were 10 years ago, but they’re engaging in sex less often and with less satisfaction, according to a major new survey by AARP.

What’s the problem?

AARP’s sex and relationship expert, sociologist Pepper Schwartz, thinks financial stress is a prime culprit.

“The economy has had an impact on these people,” she said. “They’re more liberal in their attitudes, yet they’re having sex less often. The only thing I see that’s changed in a negative direction is financial worries.”

The survey, being released Friday, is based on detailed questionnaires completed last year by 1,670 people 45 and over. AARP, which represents 40 million Americans over 50, conducted similar surveys on sexual attitudes and practices in 1999 and 2004.

One of the most pronounced changes over the 10-year span dealt with sex outside of marriage. In the 1999 survey, 41 percent of the respondents said nonmarital sex was wrong. That figure dropped to 22 percent in the new survey.

Yet sexual activity — marital or not — seems to be less frequent overall for this age group. In the new survey, 28 percent said they had intercourse at least once a week, and 40 percent at least once a month — both categories were down roughly 10 percentage points from 2004.

Asked if they were satisfied with their sex lives, 43 percent in the new survey said yes, down from 51 percent in 2004.

One intriguing finding: Respondents who had a partner but weren’t married had sex more frequently and with more satisfaction than respondents who were married.

“These long-term married couples may get a little less interested,” Schwartz said. “Older people in nonmarried relations work harder at it and enjoy it more.”

The AARP said the survey had an error margin of plus or minus 3.7 percentage points for questions answered by all respondents.