Armed with what they say is the political clout for victory, senators were continuing debate on controversial partial birth abortion legislation Tuesday.

Senator Majority Leader Bill Frist, R-Tenn., who has made the ban one of his top priorities for the GOP leadership, said he believes the odds of passing the legislation are "very good" and that a vote could be taken by the end of the week.

But abortion rights activists said they won't go down without a fight, and have already promised a court challenge if President Bush signs it into law.

"We will challenge it, absolutely, without question," said Kate Michelman, head of NARAL Pro-Choice America.

Since Republicans took over control of the Senate in last fall's elections, a ban on partial birth abortion has the best chance of passing in a decade. Congress twice passed legislation banning the procedure, in which the fetus is partially delivered before it is aborted, but former President Clinton vetoed the bill both times.

After a 63-34 vote in the Senate in 1999, Congress appeared ready to pass a third measure in 2000, but halted its efforts after the Supreme Court struck down a state law with many similarities.

Then the House passed a reworked version of the bill last year, but majority Democrats refused to schedule a debate in the Senate. The White House has already issued a statement of support of the ban, calling enactment "both morally imperative and constitutionally permissible."

Sen. Rick Santorum, R-Pa., said the legislation is aimed at banning a procedure performed only after 20 weeks of pregnancy, and described it in graphic detail. The fetus is partially delivered, he said, and then a scissor is "thrust into the base of the skull and ... the cranial contents removed."

"Just to describe it here has to send shivers down your back," he added.

He described it as a procedure that is "never medically necessary, not taught in any medical school in this country, not recommended," yet is performed more than 2,200 times a year.

But other senators said they will defend the right of women to make their own decision when it comes to partial birth abortion, and see such a ban as an encroachment upon the landmark Roe v. Wade Supreme Court decision, which legalized abortion in 1973.

"It's an attempt to outlaw all abortions, to take away a woman's right to choose ... and criminalize abortions," said Sen. Barbara Boxer, D-Calif. "And what follows from that? Women and doctors would be in jail."

Santorum insisted that the bill now on the table addressed any constitutional problems that the Supreme Court has already put forward.

But Boxer and Sen. Patty Murray, D-Wis., disagreed, saying it did not allow for exceptions to preserve the health of the mother. "The Supreme Court already ruled ... and said you cannot come to us with a bill that does not make an exception for the health of a mother."

The measure that Republicans brought to the floor bans a procedure in which a doctor commits an "overt act" designed to kill a partially delivered fetus. It also further defines "partial birth" as a case in which the entire fetal head is outside the body of the mother. If the fetus were in a breech position, the ban would apply if "any part of the fetal trunk past the navel is outside the body of the mother."

Republicans insist that the legislation includes an exemption in cases in which the procedure is necessary to save the life of the mother.

In a 5-4 ruling in 2000 that struck down a Nebraska partial birth abortion statute, the Supreme Court said that law was vaguely worded and created an undue burden on a woman's right to choose. The court also ruled that the state law was deficient because it failed to provide an exemption for the health of the mother.

However, the first 15 pages of the current Republican legislation are rhetorical, stating that a "partial birth abortion is never necessary to preserve the health of a woman, poses serious risks to a woman's health and lies outside the standard of care."

The Associated Press contributed to this report.