LOS ANGELES – Today’s teenagers are increasingly likely to use the rhythm method to prevent pregnancy and to have relaxed attitudes about unwed motherhood, a new government survey has found.

The results, released Wednesday by the National Center for Health Statistics, found that 17 percent of 15- to 19-year-olds — sexually active or not — used periodic abstinence, or the calendar rhythm method, as a form of contraception from 2006 to 2008. In 2002, 11 percent of teens used that method.

“That was pretty much a surprise,” said Joyce Abma, lead author of the study and a demographer with the center. “The rhythm method is associated with a pretty high failure rate — on average, 25 percent of women will become pregnant during the first year of using that method. It’s not a welcome development, especially in combination with the fact that overall, contraceptive use hasn’t changed significantly from the last survey.”

The poll of 2,767 teens, which was part of the National Survey of Family Growth, also found that more teens than in years past said they agreed or strongly agreed with the statement: “It is OK for an unmarried female to have a child.” Among teen boys in the current survey, 64 percent agreed or strongly agreed, while in 2002 only 50 percent did. Among teen girls that number was 71 percent, not significantly different from 2002.

Among male teens who had not yet had sex, 12 percent said the reason was that they didn’t want to get a girl pregnant. In 2002, 25 percent of male teens who had not yet had sex cited that reason. However, condom use among male teens is up — 81 percent of never-married males in the current survey said they used them at first intercourse, compared to 71 percent in 2002.

“In addition to making the means to avoid pregnancy available, we may need to go one step back and emphasize the motivations to avoid pregnancy, such as providing programs that give teens goals that are not compatible with early parenthood,” Abma said.