The Sisters of Notre Dame de Namur have issued the second and final formal warning before expulsion from the religious order to two nuns who refuse to retract their support for the right of legal abortion.

In identical Feb. 17 letters, Sister Catherine Hughes, general moderator of the order, gave Sisters Barbara Ferraro and Patricia Hussey until March 5 to promise to refrain from making any public statements that can be construed as supporting abortion.

"You know that your refusal will result in the invoking of the procedure for dismissal, and that this is our second warning letter," Hughes wrote.

The two women have steadfastly refused to retract their signatures from an Oct. 7, 1984, advertisement that said "a diversity of opinion" exists among "committed Catholics" on the abortion issue.

The advertisement, signed by nearly 100 lay and religious Catholics, appeared at the height of the 1984 presidential campaign after attacks by members of the hierarchy on Democratic vice presidential candidate Geraldine Ferraro (no relation to Sister Barbara Ferraro) and New York Gov. Mario Cuomo for refusing to commit themselves to opposing the 1973 Supreme Court decision legalizing most abortions.

Barbara Ferraro and Hussey, who work among the poor and homeless in Charleston, W.Va., received their "first canonical warning" -- the first step in formal dismissal proceedings -- on Jan. 15.

Replying to the first warning, the two said the demands placed on them by the religious order "are really an attempt to silence our consciences and our public voices on the issue of reproductive rights for women. Even with the impending threat of dismissal from the Congregation of Notre Dame," they said, "we believe we cannot abrogate our consciences on an issue that we believe is fundamental to justice for women in our society and our church."

Under church procedures, if the two do not bow to the demands by March 5, the five-member governing group of the sisters, which includes one American, Sister Elizabeth Boyer, will vote on whether to seek approval for dismissal from the Vatican's Congregation for Religious and Secular Institutes.

Ferraro and Hussey are drafting a response to the Feb. 17 letter and would not comment.

In the Feb. 17 letter, Hughes said the two sisters must, if they wish to avoid expulsion, "refrain from making any further public statements that do not fully convey your position so that the possibility of such statements being interpreted as proabortion will be minimized."