Washington ? A Bush administration lawyer urged the Supreme Court on Wednesday to uphold the nation’s first criminal ban on an abortion method, saying so-called partial-birth abortions are “too close to infanticide” and not a medical necessity.

“Safe alternatives are always available,” U.S. Solicitor General Paul D. Clement said in defending a law passed by Congress in 2003.

But two abortion-rights advocates argued that the ban, if put into effect, would unwisely limit the options of doctors who perform abortions in the second trimester and would expose some pregnant women to more dangerous surgery.

These doctors believe that the procedure medically known as dilation and extraction or D&X – in which the fetus is removed intact – “reduces the risk of serious complications,” including bleeding and infection in the uterus, said Priscilla Smith, a lawyer for the Center for Reproductive Rights in New York.

“What Congress has done here is take away from women the option of what may be the safest procedure” for some of them, said Eve Gartner, a lawyer for the Planned Parenthood Federation of America.

The oral arguments heard Wednesday could prove a turning point for the Supreme Court on abortion. With the arrival of President Bush’s two conservative appointees, there appears to be a five-vote majority to uphold stricter regulation of abortion, including Justice Anthony M. Kennedy.

Six years ago when the court struck down a Nebraska ban on the practice, Kennedy wrote an impassioned dissent, describing D&X abortions as “abhorrent.”

Now, abortion-rights advocates are hoping he will switch sides. But Wednesday, Kennedy said most midterm abortions appear to be “purely elective” and described the disputed procedure as “not medically necessary.”

New Justice Samuel A. Alito Jr. said nothing during the argument. But he and Chief Justice John Roberts have been counted as likely to uphold the federal Partial Birth Abortion Ban Act.

Even if the Supreme Court were to put into effect the new ban on “partial-birth abortions,” its influence would be limited. The disputed procedure is used only for abortions that take place after the 16th week of pregnancy. Doctors partially extract the fetus from the uterus and collapse its skull before pulling it out.

Clement described the D&X method as a “very aberrant, atypical procedure” that is not used by most abortion doctors.

Most doctors use the “dilation and evacuation” method, or D&E, in which the fetus is dismembered in the uterus before it is removed. Clement referred to this as the “gold standard” for midterm abortions.