Federal judges in New York and California blocked the law Thursday, a day after it was signed by President Bush. The rulings likely prevent enforcement of the ban nationwide until a challenge to its constitutionality can be heard.
Judge Richard Casey in Manhattan suspended the effect of the law for 10 days, saying he expected an association of abortion providers in the United States and Canada and seven doctors will succeed in their challenge. The National Abortion Federation says its members perform half of abortions nationwide.
Later in the day, U.S. District Judge Phyllis Hamilton in San Francisco ruled the law appears unconstitutional because it provides no exemptions for a woman's health, mirroring the reasons cited by the other judges and affecting doctors at 900 Planned Parenthood clinics nationwide.
The law exempts abortions necessary to save a woman's life, but not to protect her health.
The two rulings together cover a majority of the abortion providers in the United States.
On Wednesday, less than an hour after Mr. Bush signed the law, a federal judge in Nebraska made a similar ruling that covers four abortion doctors licensed in 13 states across the Midwest and East.
The Justice Department said in a statement that it "will continue to strongly defend the law prohibiting partial birth abortions using every resource necessary."
It cited arguments it made in court papers that Congress considered testimony over an eight-year period, including physicians who "uniformly agreed that a partial-birth abortion is never necessary to advance the health or life of women."
But Casey noted in his three-page order granting a temporary restraining order that a government lawyer told him at a Wednesday hearing that the medical community remains divided over the issue and that Congress did not reach a consensus.
He said the position left him with no choice but to "conclude that it is substantially likely" that the law will be found unconstitutional.
Douglas Johnson, a spokesman for the National Right to Life Committee, said the New York judge's ruling was "not surprising but it is distressing."
"It means that partly born babies will continue to die at the point of 7-inch scissors," he said. "Certainly these judicial orders severely impede the government's ability to protect these premature infants."
The new law outlaws a procedure generally performed in the second or third trimester in which a fetus is partially delivered before being killed, usually by puncturing its skull. Anti-abortion rights activists call the procedure "partial-birth abortion." President Clinton had twice vetoed similar bills.
Opponents of the law say it is overly broad, lacks any exemption for the health of a woman and could outlaw several safe and common procedures. They also contended it is the first step in a larger campaign to ban all abortions and undo Roe v. Wade, the Supreme Court's 1973 landmark decision establishing a woman's right to an abortion.
Abortion-rights advocates expect a showdown over the new law with the Bush administration at the U.S. Supreme Court.
Anthony Romero, executive director of the American Civil Liberties Union, which argued the case in New York, said the ACLU was "enormously gratified but not surprised that that law appears now to be unconstitutional."
ACLU attorney Talcott Camp said the organization got calls from worried physicians after the law took effect Wednesday without court rulings immediately nullifying its effect.
Camp said they "were indeed panicked at the prospect of having to face criminal prosecution for providing the absolute best medical care they can."
The law imposes a two-year prison sentence on doctors. A doctor who performs an abortion covered by the act, but contends it was necessary to save the mother's life, would have to prove that to a state medical board.
"We're awfully glad to be able to protect women all over the country against this dangerous, inappropriate intrusion by the government into their private, medical decision," she said.
The rulings Thursday brought relief, though "we were confident that this law would be temporarily enjoined because it is so obviously dangerous and unconstitutional," she said.
In 2000, by a 5-4 majority, the Supreme Court struck down a Nebraska late-term abortion prohibition, ruling the law was unconstitutional because it was too broad and made no exception for the health of the mother.
Abortion rights advocates say the current federal law is similarly flawed, by making provisions for the mother's life, but not her health, and by describing the banned procedure in such a way that it might be construed to ban common abortion methods used in the second trimester of pregnancy.