When the Senate takes up a bill this month to ban certain abortion procedures, the odds will be heavily against abortion-rights defenders, but they say they are still actively trying to drum up opposition to the measure.

Both Democratic Senators and abortion-rights lobbyists privately say the so-called partial-birth abortion ban bill — sponsored by Senate Republican Conference Chairman Rick Santorum (Pa.) and scheduled for possible floor action next week — will likely pass. But Democrats are still hoping a 2000 Supreme Court decision that struck down a similar Nebraska ban will convince some lawmakers to change their minds.

Both the Nebraska statute and the Santorum bill ban any abortion procedure in which the fetus is brought partially through the vaginal canal before the abortion is actually performed. Anti-abortion activists named the procedure “partial-birth abortion” and liken it to infanticide; some medical professionals call the procedure “dilation and extraction.”

Abortion-rights advocates believe their long shot could be shortened if they pick up a few Democratic votes from lawmakers who previously voted for the measure. The chief argument they’re using on these lawmakers is that voting for it now would be tantamount to ignoring the Supreme Court’s ruling.

Only 34 Senators, including three Republicans, voted against the ban in 1999. Even if abortion-rights supporters pick up 41 votes in opposition to the bill, getting those lawmakers to actually support a filibuster will be much tougher, they acknowledge.

Sens. Dianne Feinstein (D-Calif.) and Dick Durbin (D-Ill.) plan to offer alternative measures, which would ban abortions only on fetuses that would otherwise be able to live outside the womb.

Durbin is trying to decide how to write language in his bill that would allow only women with health problems to receive the so-called partial-birth abortions. Because many in the anti-abortion movement have objected to including mental health as a reason to grant an abortion, Durbin is weighing whether he can drum up more support by simply limiting the exception to physical health, said a spokesman.

Feinstein’s measure would create penalties for doctors who perform these abortions unless the doctor determines it’s necessary to save the woman’s life or protect her health.

Opponents of the ban prefer Durbin and Feinstein’s approach because they say Santorum’s bill would actually ban abortion procedures that are used on women whose fetuses are not viable — which would violate both the Supreme Court’s 1973 Roe v. Wade decision in which a woman’s right to a pre-viability abortion is guaranteed and the Nebraska case.

Santorum’s bill does not make a distinction between an abortion performed pre- or post-viability. The measure references the Nebraska case, but argues the judges erred because “partial-birth abortion is never necessary to preserve the health of a woman, poses significant health risks to a woman upon whom the procedure is performed, and is outside the standard of medical care.”