PHOENIX - A federal court should uphold Arizona's ban on abortions beyond 20 weeks of pregnancy because there is no constitutional right to abortions on demand, Maricopa County Attorney Bill Montgomery is arguing.

In filings with the 9th U.S. Circuit Court of Appeals, Montgomery, the law's chief defender, disputed the contention by foes that states cannot impose any restrictions on the ability of a woman to terminate a pregnancy before the point a fetus can live outside the womb.

Instead, he argued, women have a protection only against "undue interference" by the state. Montgomery said a law that stops virtually all abortions at 20 weeks, which is weeks before anyone contends a fetus is viable, does not cross that line.

Hanging in the balance is whether abortions at and beyond 20 weeks will become impossible for a woman to obtain in Arizona unless it is necessary to avert her death or in cases of "serious risk of substantial and irreversible impairment of a major bodily function."

Lawmakers approved the ban earlier this year, and a trial judge upheld it as legal.

But the federal appellate judges barred the state from enforcing it until they got a closer look, scheduling a hearing next month in San Francisco.

Janet Creps, an attorney for the Center for Reproductive Rights, said the constitutional rights of pregnant women were spelled out in the landmark 1973 case of Roe v. Wade, when the U.S. Supreme Court legalized abortion. The high court tinkered with that a bit in 1992, upholding a Pennsylvania law that imposes a 24-hour waiting period before an abortion can be performed as well as a requirement for a woman to be given certain information ahead of the procedure.

But Creps pointed out that the majority in the 1992 ruling said their decision has "no bearing on the validity of (Roe's) central holding, that viability marks the earliest point at which the state's interest in fetal life is constitutionally adequate to justify a legislative ban on nontherapeutic abortions."

Montgomery conceded that's what the high court said, and said he's not urging the appellate court to ignore the two precedent-setting rulings. But he is trying to craft a way around them, saying, in essence, the situation is different now.

"(The earlier rulings) continued to assume the comparative safety of abortion over childbirth," Montgomery wrote. "And they were not informed of current medical knowledge that the unborn child feels pain," an argument presented to lawmakers by some medical professionals and disputed by others.

If that argument does not work, Montgomery has another one. He said the legislation does not violate the Supreme Court rulings because it does not ban all pre-viability abortions. Instead, he argued, it simply regulates it, citing the exception for maternal life and health.

Creps, however, argued the judges cannot uphold the law based on a narrow exception. Prior to the viability of a fetus, "it is the woman - not Arizona - who decides whether and when she will terminate her pregnancy," Creps said.