WASHINGTON -- The U.S. House of Representatives passed a far-reaching anti-abortion bill that conservatives saw as a milestone in their 40-year campaign against legalized abortion and Democrats condemned as another example of what they see as Republicans' war on women.

The legislation, sparked by the murder conviction of a Philadelphia late-term abortion provider, would restrict almost all abortions to the first 20 weeks after conception, defying laws in most states that allow abortions up to when the fetus becomes viable, usually considered to be around 24 weeks.

The legislation lays further groundwork for the ongoing legal battle that abortion foes hope will eventually result in forcing the Supreme Court to reconsider its landmark 1973 decision, Roe v. Wade, that made abortion legal.

In the short term, though, the bill will go nowhere. The Democratic-controlled Senate will ignore it, and the White House says the president would veto it if it ever reached his desk. The White House said the measure was "an assault on a woman's right to choose."

But it was a banner day for social conservatives. Penny Nance, president of Concerned Women for America, called it "the most important pro-life bill to be considered by the U.S. Congress in the last 10 years."

Democratic leader Nancy Pelosi called the legislation "yet another Republican attempt to endanger women."

Democrats repeatedly pointed out that all 23 Republicans on the chamber's Judiciary Committee that approved the measure last week are men.

The Republican leadership moved ahead on the abortion bill after the case of Kermit Gosnell, the Philadelphia abortion doctor who was recently sentenced to life in prison for what prosecutors said was the murder of three babies delivered alive. Abortion foes said it exemplified the inhumanity of late-term abortions.

Some 10 states have passed laws similar to the House bill, and several are facing court challenges. Last month a federal court struck down as unconstitutional Arizona's law.

According to the Guttmacher Institute, a New York-based reproductive health research organization that supports abortion rights, 1.3 per cent of the 1.2 million abortions in the country in 2009 -- about 15,600 -- occurred 20 weeks after the fetus was conceived.

Supporters of the legislation also contended that fetuses can feel pain after about 20 weeks. Opponents say such findings are inconclusive.