(Adds Planned Parenthood closing one Texas clinic)
By Karen Brooks
AUSTIN, Texas, July 18 (Reuters) - Texas Governor Rick Perry on Thursday signed into law tough new restrictions on abortion, including a ban after 20 weeks of pregnancy, marking one of the biggest victories in a decade for opponents of the procedure in the United States.
Perry, a Republican, signed the measure flanked by invited political supporters and anti-abortion activists, who gave him a standing ovation as he entered the room.
"It is a very happy and celebratory day," said Perry, who thanked anti-abortion activists for helping to "support the health of Texas women."
Outside, about two dozen protesters dressed in black shouted "Shame," and "The blood of Texas women is on your hands!"
Republican lawmaker Jodie Laubenberg, who sponsored the bill, said "the hand of God" had allowed her and others to overcome fierce opposition and pass the measure in the Texas legislature.
Cherie Weaver, wearing a black dress to protest the law, said democracy had failed Texas women. "The separation of church and state has been completely undermined in this fight," she said, referring to the U.S. tradition of keeping government and religion at arms length.
The Roman Catholic church officially opposes abortion as do many conservative Protestants.
Texas Republicans, who have a large majority in the state legislature, pushed through the restrictions over the fierce objection of Democrats and supporters of the right to abortion.
Democratic state Senator Wendy Davis briefly caught national attention last month by staging a filibuster to stall the restrictions, although her gambit ultimately failed.
"When Governor Perry signed the bill, he signaled a clear break with Texas families," Davis said in a statement, adding that Perry was siding with "special interests" over women's health.
Supporters of abortion rights have vowed to challenge the law in court.
"We believe parts of this law are unconstitutional and are working to stop it from taking effect," Cecile Richards, President of Planned Parenthood Action Fund, said in a post on twitter. Planned Parenthood is the nation's largest abortion provider.
Several other conservative states have approved piecemeal abortion restrictions, but Texas is by far the most populous and politically important, and it took more dramatic action by combining several measures into one bill.
The Texas measures are also more far reaching than a ban passed by the U.S. Congress in 2003 on a type of late-term abortion called "partial birth," which covered only a small fraction of abortions performed each year.
Texas joined 12 other states that have passed bans on abortion after 20 weeks, citing disputed research that a fetus feels pain by that stage. North Dakota and Arkansas have gone further, banning abortion as early as six and 12 weeks, respectively. (For factbox, see )
The current limit for abortions in Texas is 26 weeks.
Texas is also requiring all abortion facilities to meet by September 2014 the same standards as outpatient surgery centers, and forcing doctors performing abortions to have the right to admit a patient to a hospital within 30 miles of a clinic.
The law will prohibit anyone other than a doctor dispensing the so-called "abortion pill," or RU-486 drug, to end pregnancies, and require that a second dosage be administered at a clinic under a doctor's supervision and not at home.
Texas already has a law passed two years ago requiring a woman to undergo an ultrasound and be shown the results, before an abortion can be performed.
Opponents of the new Texas law say it will be found unconstitutional because the landmark Roe v. Wade Supreme Court decision in 1973 allowed abortion up to the point a fetus is viable, or can live outside the womb.
Supporters of the Texas law say technology for treating premature babies has resulted in survival at earlier stages of gestation. They say that the government has a compelling right to protect the fetus as early as 20 weeks.
The Republican-led U.S. House of Representatives last month passed a ban on abortion after 20 weeks, although the measure has little chance of passage in the Democratic majority Senate.
Planned Parenthood and other operators of clinics have warned that only a handful of the 42 facilities in Texas providing abortions now meet the standards set in the new law, and the cost of upgrading could force dozens to close. Supporters of the law have said that is an exaggeration.
Within hours of Perry signing the law, Planned Parenthood said it would close one of its 13 centers providing abortions in Texas because of the new requirements.
Some legal challenges of other state laws have been successful. A federal judge on Wednesday extended for two more weeks a hold on a Wisconsin provision requiring doctors performing abortions to have admitting privileges at a hospital, while the judge studies whether to block the law.
The U.S. Supreme Court has not ruled recently on an abortion case. In 2006 it narrowly endorsed, 5 to 4, the U.S. Congressional ban on "partial birth" abortions. (Reporting by Karen Brooks; Additional reportig by Lisa Maria Garza in Dallas; Writing by Greg McCune; Editing by Andrew Hay)