NEW YORK — Judith Kaplan Eisenstein, the mother of the bat mitzvah and the daughter of one of the 20th century's most influential theologians, has died.

Kaplan Eisenstein, who was also a noted authority on Jewish music as well as a composer and lyricist, died Wednesday of a heart attack at age 86 while in a Rockville, Md., hospital recovering from a broken hip.

Those who knew her remembered her as a vibrant woman with a strong will and a deep commitment to Judaism the way her father, Rabbi Mordecai Kaplan, articulated it — as an evolving civilization.

The oldest of the theologian's four daughters, Kaplan Eisenstein was encouraged by her father to question and challenge Orthodox views.

"When I was 11, I told my father that I didn't believe in God," she recalled during an interview in 1994.

"There was a sense of freedom and freedom to change. There was a constant opening up of possibilities and enrichment" with his view of Judaism, she said.

"It made my being Jewish a great joy for me rather than a burden," she said.

At the age of 12, and under her father's tutelage, she completed the very first bat mitzvah at the newly founded Society for the Advancement of Judaism in Manhattan.

Her father had thought of the idea only a day before. That night, she practiced reading the Torah portion with him.

"I didn't work on it the way kids work on it now, for a half year with lessons every week," she said in 1992, shortly before her accomplishment was celebrated again 70 years later.

"All I did was read it through with him Friday night, and Saturday morning I went into the synagogue and did it," she said.

The ceremony pro-ved to be a revolutionary breakthrough.

Today all but the most stringently Or-thodox girls celebrate their bat mitzvah in some form.

Reform, Conservative and Reconstructionist girls are called to the Torah during synagogue services and generally give a sermon as well.

Many Orthodox girls mark the day by speaking to the women of the congregation about the Torah portion of the week. There often is a festive party, as well.

Even more significant for many is the fact that Kaplan Eisenstein's bat mitzvah was the first time that a female had stood before the congregation as a leader.

"It was an opening of opportunities, dreams that suddenly become available," said Rabbi Shohama Wiener, president of The Academy for Jewish Religion, an independent rabbinical and cantorial seminary located in Manhattan, just down the street from the Reconstructionist synagogue founded by Mordecai Kaplan.

Kaplan Eisenstein earned bachelor's and master's degrees in music from Columbia University.

From 1929 to 1954, she taught music education and the history of Jewish music at the Jewish Theological Seminary. She published a book of children's music, "Gateway to Jewish Song," which quickly became a staple of teachers of Jewish nursery school.

In 1934, Kaplan Eisenstein married her father's closest disciple, Ira Eisenstein, who was working as Kaplan's assistant rabbi at the Society for the Advancement of Judaism.

She began writing cantatas rooted in Judaism in 1942, and ultimately published seven, some in collaboration with her husband.

While in her 50s, she earned a doctorate at the Hebrew Union College-Jewish Institute of Religion's School of Sacred Music.

She published a book on the history of Jewish music, "Heritage of Jewish Music," which is still in print and widely read.

Kaplan Eisenstein taught music at that Reform movement seminary and at the Reconstructionist Rabbinical College, which was founded by her husband in Philadelphia in 1968.

She reminded Reconstructionist Jews of the importance of music and the arts in living a life committed to Judaism, said Rabbi Mordechai Liebling, executive director of the Jewish Reconstructionist Federation, which is based in Wyncote, Pa.

She and her husband were popular teachers at the Reconstructionist Rabbinical College community until they retired to Woodstock, N.Y., in 1980.

In the house where they had spent weekends for many years, in a town where there was no organized Jewish community, they started a chavurah, a prayer and study group.

"They brought in old lefties and musicians and artists who wouldn't be caught dead in a synagogue," said Jonathan Kligler, a Reconstructionist rabbi and spiritual leader of Kehillat Lev Shalem-The Woodstock Jewish Congregation, founded 10 years ago.

"They got this group of Jews together and made a real chevra [group of friends] out of them," said Kligler, who took over leading the chavurah when the couple moved to Silver Spring, Md., last September to be near one of their daughters.

The 62-year-marriage of Kaplan Eisenstein and Ira Eisenstein, who is now 89, is viewed by many who have known them as a great pairing of two powerful souls.

In addition to her husband, Kaplan Eisenstein is survived by two daughters, three sisters and a grandchild.

She was buried at the Judean Memorial Gardens in Rockville.