The proportion of American teenage girls and women having sex climbed in the 1980s, but the pregnancy rate changed little because of increased use of condoms, a study found.

"All the publicity about using condoms has had some impact," said Susheela Singh, co-author of the Alan Guttmacher Institute study released Wednesday.The study of sexual behavior from 1982 to 1988 also found one of every five teenagers having sex in 1988 used no birth control.

Among poor teenagers, one in four failed to use contraceptives during intercourse and one-third of all young women are still unprotected from pregnancy the first time they have sex, the study found.

The proportion of girls ages 15 to 19 who had sexual intercourse rose from 47 percent in 1982 to 53 percent in 1988, the study found. The increase was greatest among whites and in higher-income families.

In 1982, the proportion of whites who were sexually active was 45 percent, compared to 52 percent in 1988. The increase among teenagers in families with income of more than 200 percent of the poverty line was from 40 percent to 50 percent.

"The levels of sexual activity were already high among non-white and poor girls," Singh said. "The white and non-poor are catching up as attitudes change and become more liberal."

The study found that 58 percent of the overall sexually active group reported having intercourse with two or more partners.

According to the study, 48 percent used a contraceptive method at first intercourse in 1982, mainly a condom, compared to 65 percent in 1988. Regular condom use jumped 25 percentage points to 47 percent, it said.

"Thus male involvement in contraceptive use at first intercourse increased substantially," the study found.

The study also found that 57 percent of all pregnancies conceived in 1987 were unintended. While that is about the same as in 1982, the proportion of unintended pregnancies terminated by abortion fell, from 54 percent in 1982 to 50 percent in 1987.

Among teenagers there were 127 pregnancies per 1,000 women in both 1982 and 1988, according to the study.

The institute's study is based on data released in the spring by the National Center for Health Statistics. The National Survey of Family Growth compiled the 1988 data from interviews with 8,450 women; a total of 7,969 women were interviewed in 1982.