PHOENIX - Calling a woman's rights "unalterably clear," a federal appeals court on Tuesday struck down Arizona's nearly year-old ban on abortions at 20 weeks and beyond.

In a unanimous decision, the 9th Circuit Court of Appeals acknowledged the law on what states can and cannot restrict has varied since the landmark 1973 ruling in Roe v. Wade. That ruling barred states from banning a woman's right to an abortion, at least early in her pregnancy.

But Judge Marsha Berzon, writing for the court, said one thing has remained constant.

"A woman has a constitutional right to choose to terminate her pregnancy before the fetus is viable," she said, something attorneys for the state concede does not occur before 23 or 24 weeks. "A prohibition on the exercise of that right is per se unconstitutional."

While a federal judge last year declared the law valid, it has never been enforced because the appellate court put it on hold while it considered the appeal.

Maricopa County Attorney Bill Montgomery, who personally argued the case, said he will seek U.S. Supreme Court review.

Montgomery said he believes the justices will conclude the state has a right to impose restrictions - even strict ones - on abortions for legitimate reasons.

He said evidence presented to lawmakers was a fetus can feel pain at 20 weeks. He said there also was testimony the procedure is more risky for a woman at that point in her pregnancy or beyond.

But Berzon said no amount of argument from Montgomery can overcome the fact the Arizona law is not an acceptable restriction.

"Since Roe, the Supreme Court and lower federal courts have repeated over and over again that viability remains the fulcrum of the balance between a pregnant woman's right to control her body and the state's interest in preventing her from undergoing an abortion," Berzon wrote. And because it is a ban, and not merely a limitation, "no state interest is strong enough to support it."

Cathi Herrod, president of the anti-abortion Center for Arizona Policy, said she is "not surprised or discouraged."

"The 9th Circuit Court of Appeals is well known for opinions that get overturned by the United States Supreme Court," she said.

Matthew Benson, press aide to Gov. Jan Brewer, who signed the legislation last year, said the governor supports appeal of this "misguided ruling."

In a concurring opinion, Judge Andrew Kleinfeld brushed aside the measure's stated interest in protecting a woman's health as a reason to keep her from getting an abortion at or after 20 weeks.

"People are free to do many things to their health, such as surgery to improve their quality of life but unnecessary to preserve life," Kleinfeld said. "There appears to be no authority for making an exception to this general liberty regarding one's own health for abortion."

He also said there may be legal ways for the state to deal with its stated concerns about fetal pain.

"Were the statute limited to protecting fetuses from unnecessary infliction of excruciating pain before their death, Arizona might regulate abortions at or after 20 weeks by requiring anesthetization of the fetuses about to be killed, much as it requires anesthetization of prisoners prior to killing them when the death penalty is carried out," Kleinfeld wrote.

Montgomery said that proves his point that total deference to a woman's choice prior to viability is not an acceptable standard. He said that if a fetus has pain receptors like an adult, just minus the ability to control that pain, "it does require us to face to what degree are we going to acknowledge that humanity has expressed in that life that we're willing to authorize someone to take life in that way."

Kleinfeld acknowledged the problem with using viability to determine when a state can and cannot ban abortion.

He pointed out that was considered 28 weeks in 1973. And he said medical science for premature babies may advance to where they are viable three or four weeks earlier than they are now.

But Kleinfeld said the court has to decide the legal issue based on current science.

"The 9th Circuit got it exactly right," said Janet Crepps, the attorney for the Center for Reproductive Rights, which challenged the law.

"When you tell somebody that they are absolutely forbidden to do something, that's a ban," Crepps said.

Kleinfeld also said the fact that an Arizona woman wanting an abortion at or after 20 weeks can go to another state does not make the law any more unacceptable.