San Francisco ? The legal attack against a new ban on certain late-term abortions rapidly escalated Thursday as federal judges in New York and California blocked the law, delivering a major setback to President Bush only a day after he signed the measure.

The ruling by the San Francisco judge affects doctors who work at 900 Planned Parenthood clinics nationwide. The decision and the ruling in New York hours earlier together cover a majority of the abortion providers in the United States.

And on Wednesday, a federal judge in Nebraska made a similar ruling that covers four abortion doctors licensed in 13 states across the Midwest and East. The ruling came less than an hour after Bush signed the law.

The rulings prevent enforcement of the ban until a challenge to the law’s constitutionality can be heard.

The 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 activists call the procedure “partial-birth abortion.” President Clinton twice vetoed similar bills.

Opponents of the law said it was overly broad, lacked any exemption for the health of a woman seeking an abortion 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. Wave, 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.

The Justice Department said in a statement that it “will continue to strongly defend the law prohibiting partial birth abortions using every resource necessary.”

U.S. District Judge Phyllis Hamilton of San Francisco ruled the law appears unconstitutional because it provides no exemptions for a woman’s health.