US abortion opponents are hoping for a national ban on a widely used abortion pill when their lawsuit against government drug regulators is argued on Wednesday in the Texas court of a deeply conservative judge believed to be sympathetic to their cause.

Galvanised after the US Supreme Court ended the nationwide right to abortion last June, anti-abortion forces are now targeting the prescription drug mifepristone in their campaign to win a total ban on the practice.

The suit against the US Food and Drug Administration (FDA) aims at a pill involved in 53 percent of all abortions in the United States, or more than a half-million every year.

While the FDA has never been challenged like this before on its approval of a drug that has proven safe and effective, the plaintiffs, a coalition of anti-abortion groups, believe they can win a national freeze on distribution of mifepristone.

Presiding over the case in federal court in Amarillo, Texas will be Judge Matthew Kacsmaryk, a deeply conservative Christian with a personal history of opposition to abortion and a court record of favoring right-wing causes.

The case ended up in his court via what critics call "judge-shopping", in which plaintiffs take legal action in a district where the judge has a history of rulings that support their case.

One component of a two-drug regimen used for medication abortion, mifepristone can be used in the United States up to 10 weeks of pregnancy.

It has a long safety record, and the FDA estimates 5.6 million Americans have used it to terminate pregnancies since it was approved.

But the Alliance Defending Freedom, a Christian advocacy group, sued the FDA saying the approval of mifepristone "disavow(ed)" science, "ignored" potential health impacts and "disregarded" the complications that can arise with its use.

"The FDA failed America's women and girls when it chose politics over science and approved chemical abortion drugs for use in the United States," they said.

The FDA has urged the judge to reject the request.

"The public interest would be dramatically harmed by effectively withdrawing from the marketplace a safe and effective drug that has lawfully been on the market for 22 years," it said. (AFP)