The ordination of women as rabbis in Conservative Judaism, the largest branch of Judaism in this country, was unexpectedly vetoed Thursday by a vote of the faculty of the Jewish Theological Seminary in New York City.

The faculty of Conservative Judaism's only rabbinical training institution in this country voted 25 to 18 to table a motion to admit women to its rabbinical training program, "in effect, a defeat of the move to ordain women," said Dr. Gerson Cohen, the school's chancellor.

Women trained in other institutions could conceivably still apply for ordination as Conservative rabbis -- and there are, in fact, two women serving Conservative congregations in this country. But the vote of the seminary faculty effectively closes the main door of the Conservative rabbinate to women.

Last January, a special commission of the Rabbinical Assembly, the movement's rabbis' organization, concluded a two-year study of the issue by recommending that women be ordained. Only three of the 14-member study commission dissented.

But the Assembly deferred to the Seminary for the final decision, a reflection of the rabbis' veneration of scholarship -- particularly where matters of Jewish law are concerned. Because the seminary is the only rabbinical training school in this country for Conservative rabbis, it has close ties with the Rabbinical Assembly, which in turn is a sort of alumni association of the seminary.

At that time, Rabbi Wolfe Kelman of New York, executive vice president of the assembly, estimated that "there may be 100 [of the 1,100 Conservative rabbis in this country] who feel very, very strongly" that women should not be ordained.

In th intervening months, however, the traditionalists have mobilized and threatened to organize a separate wing of Conservative Judaism if women were admitted as rabbis.

This traditionalist move climaxed in a conference of 170 rabbis called earlier this week to pledge their commitment to the interpretation of ancient Jewish law that, they say, precludes ordaining women.

Meanwhile, 16 of the seminary's faculty said last week that they would refuse to vote on the question because they feared it would split the Conservative movement.

Accordingly, the proposal that the faculty senate approved yesterday noted that the issue "threatens to inflict irreparable damage to the academic excellence of the seminary" as well as the unity of Conservative Judaism. The proposal said the matter should be tabled for "systematic study."

Cohen, who has been an outspoken advocate of ordaining women, said yesterday he will call a January meeting of students and faculty to assess the situation and consider further steps.

Nearly half the 500 students of the seminary are women, but all are enrolled in programs other than rabbinical studies.

Rabbi Seymour Siegel of the seminary faculty and an expert on Jewish law, said after the vote that a woman "trained [as a rabbi] in another institution could apply for membership in the Rabbinical Assembly," which functions as the certifying body of rabbis for Conservative congregations.

Conservative congregations in Coatesville, Pa., and Indianapolis currently are being served by women rabbis trained in Reform or reconstructionist seminaries, Siegel said. The United Synagogue of America, the congregational arm of the Conservative movement, has endorsed ordaining women.

About a dozen women rabbis, with several times that number in training, are serving the more liberal Reform or Reconstructionist congregations.