Relations between Christians and Jews are better today than they have been for 2,000 years, a rabbinical expert on the subject said here last week.

Rabbi Marc Tanenbaum said the action of the Second Vatican Council nearly 20 years ago in ruling that the Jewish people were not responsible for killing Christ "uprooted for all time the source of anti-Semitism. That was the greatest step in Christian-Jewish relations in 2,000 years," he said, and opened the way for dialogue and cooperation between the two religious groups.

Tanenbaum, interreligious affairs director for the American Jewish Committee, said in a Sabbath service at Washington Hebrew Congregation here that the Jewish community's "greatest allies in the world today in combating anti-Semitism are the Roman Catholic Church and Christian people of good will in every city of the United States and throughout the western world."

A Roman Catholic priest who joined Tanenbaum at the service, which was part of the committee's 75th anniversary meeting here, denounced fellow Christians, Protestant and Catholic, who criticize Israel.

Calling Israel "the litmus test of the Christian attitude toward Jews and the Jewish-Christian dialogue," the Rev. Edward Flannery said that "many Christians fail the test . . . . Too many tend to judge [Israel] severely, critize it unfairly, tend to apply an artificial evenhandedness to the Arab-Israeli conflict and even to favor Israel's enemies."

He speculated that "an anti-Zionist feeling or ideology, Arab propaganda, oil politics, or even an unacknowledged anti-Semitism" might be responsible for such attitudes.

Flannery, now an official of the Roman Catholic Diocese of Providence, was head of the Catholic-Jewish relations department of the National Conference of Catholic Bishops during 1967-76. A conference official said this week that Flannery does not speak for the hierarchy on Israel.

Flannery faulted his own church, for not supporting Jerusalem as "an undivided and Jewish city," and the Protestant National Council of Churches, for its "artificial evenhandedness" in public statements on the Arab-Israel conflict.

In a bitterly debated policy statement adopted a year ago, the NCC called for recognition by each side of the other's right in the ongoing dispute. It advocated negotiation as the means of settling differences between Israel and the Palestine Liberation Organization, but only after the PLO recognized Israel as a sovereign Jewish state.

Flannery charged that "by their very evenhandedness," the National Council of Churches throws "their weight, will it or not, to the side of the claims of Israel's enemies."

He also faulted Catholic calls for involving the PLO in Middle East negotiations. "I cannot understand why religious bodies should risk giving encouragement to self-proclaimed destroyers of Israel by sitting down with them or urging others to do so," he said.

In his remarks, Tanenbaum praised the priest's address, referring to him as "Rabbi Flannery." He added that "Father Flannery has delivered the Jewish speech this evening."

In terms of interfaith cooperation, Tanenbaum said, "We have come far, but we have still further to go." Referring to the assassination attempt on Pope John Paul II "by terrorist bullets," the rabbi challenged Christians and Jews to work together to confront "the grave epidemic of dehumanization in the world, the idea that human life is expendable."