Yosef Y. Kazen, a Hasidic rabbi who pioneered the use of the Internet as a powerful recruiting and educational tool for the Lubavitch movement, died Dec. 1 at New York Hospital. He was 44 and lived in Crown Heights, Brooklyn.

The cause was complications of non-Hodgkins lymphoma, said Moshe Kotlarski, his brother-in-law and the development director at the Lubavitch World Headquarters in Brooklyn.

The Hasidic branch of Judaism is rooted in the mysticism of 18th century Eastern Europe, but the Lubavitch movement has long used modern means to propagate its teachings, and Rabbi Kazen staked a claim in cyberspace in the late 1980's, before the World Wide Web existed.

An early user of computer bulletin boards, he was inspired by the notion of adding a 24-hour, on-line Web site to the movement's worldwide network of outreach and study centers. He digitized and made thousands of documents available on the Web, including an English translation of the Tanya, a seminal text of Jewish mysticism, and the writings of Rabbi Menachem Schneerson, the Lubavitcher spiritual leader, who died in 1994.

With the growth of the Web's popularity, Rabbi Kazen's Internet site, Chabad-Lubavitch in Cyberspace, served as a model for other Jewish organizations, who created their own educational Web sites. Visitors to www.chabad.org can read articles on science and Judaism, listen to religious melodies and browse a gallery displaying the work of Hasidic artists.

In addition to building a Jewish library on the Web, Rabbi Kazen sought to create an on-line congregation and to answer questions by E-mail, operating first from his own basement and later from a cramped office at the Lubavitch headquarters. His Internet activities varied from helping to organize a Passover service held on a boat near Antarctica to dispatching kosher recipes to Jews living far from centers of Jewish population.

Rabbi Kazen developed automated responses to the most frequently asked questions and responded personally to some messages, like the E-mail from a student in New Mexico who wanted to know whether it was permissible to smoke marijuana on the morning of the Sabbath. ''I wrote him back that, within Judaism, the concept is that the prayer itself gives you the high,'' the rabbi told Jeff Zaleski, author of ''The Soul of Cyberspace'' (1997).

In his last months, Rabbi Kazen kept a laptop computer in his room at New York Hospital so he could continue his electronic correspondence.

Rabbi Kazen was born in Cleveland and grew up there in a Yiddish-speaking household, the son of Russian immigrants and the youngest of seven siblings. He became a rabbi at the United Lubavitcher Yeshivoth in New York. A heavy-set man with a carrot-colored beard, he was also at the forefront of the more traditional Lubavitch outreach programs, which include the ''Mitzvah tanks,'' the vans and trucks that dispense both prayer books and tefillin (boxes containing passages from Scripture worn during prayer).

He saw distinct advantages in adapting new technologies to an ancient purpose.

''Some guy in a black hat and tefillin comes to you, and you have the stereotype,'' Rabbi Kazen said in an interview in The New York Times in 1994. ''When you go to the Internet and you read about Judaism, you go straight to the intellect and the stereotypes fall away.''

Rabbi Kazen is survived by his wife, Rochel; six children, Raizel, Michoel, Shmuel, Elchanan, Peretz and Sarah; his parents, Rabbi Zalman and Shifra Shula Kazen, of Cleveland; and six sisters, Esther Alpern of Sao Paulo, Brazil; Devorah Alevsky of Cleveland; Henya Laine of Brooklyn; Bluma Weinberg of Kansas City, Kan.; Rivkah Kotlarsky of Brooklyn, and Rochel Goldman of Johannesburg.