Trials began in federal courtrooms in three states Monday as abortion-rights activists sought to have the new federal ban on partial-birth abortion (search) declared unconstitutional.

The trials — in New York, San Francisco and Lincoln, Neb. — are the first to dispute the law President Bush signed in November that bans the controversial late-term abortion procedure.

In the opening statements of the New York case, the government contended that fetuses feel pain during partial-birth abortions and that the procedure therefore should be illegal.

Click here to read the Partial-Birth Abortion Ban Act of 2003.

Assistant U.S. Attorney Sean H. Lane defended the federal ban, which he described as an attempt to stop an "inhumane and gruesome procedure that causes pain to the fetus."

But a lawyer for the plaintiffs argued that making some abortions illegal poses a threat to all late-term abortions and violates constitutional rights. A. Stephen Hut Jr., the plaintiffs' attorney, said the law is overly vague and should be taken off the books.

"Our evidence will show the court that this act unconstitutionally compromises a woman's right to reproductive choice and it is designed to remove the abortion alternatives," Hut told the court.

To date, the federal law has not yet been enforced because judges in the three cities agreed to hear evidence in the separate trials without juries before deciding whether it violates the Constitution.

Judges in the three cities will hear from the National Abortion Federation (search), the Planned Parenthood Federation of America (search) and several doctors that the law was written too broadly and vaguely, and in such a way that it threatens the health of some mothers.

The simultaneous litigation centers on the ban of what lawmakers defined as "partial-birth" abortion and what doctors call "intact dilation and extraction" — or D&X.

The Partial-Birth Abortion Act (search) carries a maximum two-year prison term for doctors convicted of performing the procedure. The litigation appears likely to reach the Supreme Court.

In the procedure, generally performed in the second trimester and occasionally in the third, a fetus is partially delivered and its skull is punctured. An estimated 2,200 to 5,000 such abortions are performed annually in the United States, out of 1.3 million total abortions.

Critics of the law say its language could criminalize more common types of abortion and could be a step toward abolishing abortion. Supporters contend it applies only to a procedure done late in pregnancy that is never necessary to protect the health of the mother.

Hut warned that evidence in the trial will include "very raw stuff" and that descriptions of surgery were "not for the faint of heart." But he said that the federal ban was hazy and unconstitutional and therefore should be tossed.

The government said partial-birth abortions aren't ever required medically, as defenders have advocated, and because of the nature of the procedure, doctors shouldn't be allowed to perform it.

"Evidence at trial will illuminate that partial-birth abortion is never medically necessary and is an inhumane procedure that should be banned," Lane said.

And he said the law was specific in banning an abortion procedure that kills a "partially born fetus just inches from birth."

Abortion-rights supporters say the partial-birth ban, the first substantial limitation on abortion since the Supreme Court's landmark Roe v. Wade (search) decision, violates that ruling.

The high court struck down a similar Nebraska law almost four years ago because it lacked an exception for procedures done to preserve a woman's health. Anticipating this problem, Congress declared that "a partial birth abortion is never necessary to preserve the health of a woman" and is "outside the standard of medical care."

The abortion-rights groups disagree, saying that doctors may find themselves with no good alternative to the banned procedure to protect a woman's life or health if problems develop.

The American Medical Association does not encourage use of D&X, but says it should not be banned. The College of Obstetricians and Gynecologists says alternatives to D&X usually exist, but that in some circumstances it may be the best procedure.

Opponents of the ban also argue that its language is vague and could be interpreted as covering more common, less controversial procedures, including "dilation and evacuation." Known as D&E, it is the most common method of second-trimester abortion. An estimated 140,000 D&Es take place in the United States annually.

The Associated Press contributed to this report.