LOS ANGELES (AP) _ Medical advances that make it possible for increasingly premature fetuses to survive outside the womb raise questions about the time in which women have a legal right to abortions, a panel of experts said Tuesday.

Abortion foes are using the survivability of younger fetuses to bolster their argument against the 1 percent of abortions that occur after the 20th week of pregnancy, said Nan Hunter of the American Civil Liberties Union.

''The idea of earlier viability (of fetuses) has gotten more attention than any realistic shift that has happened,'' Ms. Hunter said. ''There is a danger that such (medical) advances will encroach on a woman's right to terminate a pregnancy.''

''The problem actually, to be blunt, is a political one,'' she said during a news conference at the annual meeting of the American Association for the Advancement of Science.

The U.S. Supreme Court's 1973 Roe vs. Wade decision held that states cannot limit abortions in the first trimester of pregnancy. But it also allowed states to prohibit abortions when the fetus is considered able to survive outside the womb with the aid of life-support equipment, said Nancy K. Rhoden, an assistant professor at the Ohio State University Law School.

At the time of that ruling, fetuses were considered viable after the 28th week of pregnancy, Ms. Hunter said.

But with subsequent advances in intensive medical care of newborns, ''we have been approaching the 24th week as a point of viability,'' said Dr. Robert Hayashi, chief of obstetrics at Harbor-UCLA Medical Center.

Fetuses even younger than 24 weeks may be considered as having a chance for survival in future years if doctors learn to enhance development of such infants' premature lungs and perhaps develop an artificial womb to keep them alive, he added.

The trend toward survival of younger fetuses, coupled with recently developed techniques to perform corrective surgery on unborn fetuses, means doctors increasingly view the fetus as a patient, said Hayashi and Vicki Michel, an ethics expert at Loyola Law School in Beverly Hills.

Ms. Michel said the trend raises the question of whether a woman would be obligated to allow life-saving treatment of a fetus she wanted to abort but that was born alive. She said it also raises questions of whether doctors are obliged to use all possible methods to save a fetus that survives abortion and to use abortion techniques that minimize the chance of killing the fetus.

''It's just a horrible situation when the abortus (aborted fetus) is delivered and begins to move around and breathe and have a heart beat,'' Hayashi said. He said his hospital's policy in such cases is to keep the infant warm and on a respirator, but not to take extraordinary life-saving measures.

''Different hospitals and different clinics have different policies,'' Ms. Hunter said.

In one abortion ruling by the Supreme Court, Justice Sandra Day O'Connor wrote a dissent suggesting medical advances might render fetuses viable as early as the first trimester of pregnancy - 13 or 14 weeks - in the not-too- distant future.

Ms. Rhoden said that was unlikely.