''JM in the AM'' is unapologetically Orthodox, with rightward leanings. Now in its 18th year, the show stands out at WFMU (91.1), the Jersey City station that celebrates itself as ''freeform'' radio, playing everything from blues to waltzes to yodeling. WFMU prides itself on being unpredictable -- except from 6 a.m. to 9 a.m., drive time, when Mr. Segal presides over ''JM in the AM,'' which stands for Jewish Moments in the Morning.

Rabbi Lookstein, the former president of the New York Board of Rabbis and longtime principal of a modern Orthodox day school in Manhattan known as Ramaz, said that he was glad that Mr. Segal did not take his advice of years ago and pursue the rabbinate. ''I think Nachum Segal is one of the best things that's happened to radio as far as our young people are concerned,'' he said. ''He's full of good values, gives them a certain amount of news and plays beautiful music.''

''I think it's a great counterforce to 'Imus in the Morning' and Howard Stern,'' the rabbi added.

Other Jewish educators, as well as musicians, however, feel that the program has moved too aggressively to cater to the Orthodox right. They note that fewer and fewer female vocal artists are heard on his program (women's singing voices are not welcome in some Orthodox circles), that Mr. Segal's political preferences, especially when they relate to Israel, are increasingly hard-line, and that serious Jewish choral music is passed over in favor of what his critics call unsophisticated ''yay-di-dai'' Hasidic and yeshiva tunes. Still, few are willing to criticize him openly for fear that their CD's, concerts and events will not get air time. ''He's the only game in town,'' a person active in a modern Orthodox group said.

Mr. Segal, who is 37, acknowledges that he is right of center on Israeli politics; for example, he is not sympathetic to Prime Minister Ehud Barak's latest peace initiatives. But he added, ''My politics are very typical of the young Orthodox person today.'' His music choices are also in tune with the tastes of his audience, he said; the Hasidic and yeshivish tunes are more popular than Jewish choral music. ''It's what the young people want to hear,'' he said.

Jewish radio is a niche market. It has not blossomed to become a major community force the way that black radio, for example, has succeeded, with its own networks and talk and music shows. Aside from Mr. Segal's show, the only other major daily Jewish radio program in New York is the talk show broadcast by Zev Brenner weeknights on WPAT-AM (930) and on Saturday nights on WMCA-AM (570), a Christian radio station owned by the Salem Radio Network. Mr. Brenner's are commercial programs, supported largely by Jewish advertisers. Mr. Segal also has a commercial show, ''The Nachum Segal Show,'' on Monday through Thursday nights at 7 on WNSW-AM (1430), and supplements his income by serving as a master of ceremonies at Jewish concerts and dinners.

But Mr. Segal made his mark on WFMU. ''I can't consider the station without him,'' said Ken Freedman, the general manager of WFMU. ''Nachum's part of the chemistry of the station.''

He's also a large part of the station's finances. Ten years ago, contributions from ''JM in the AM'' listeners accounted for one-third of the station's revenues. Today, that percentage is down to about 11 percent, Mr. Freedman said, because the station has been successful in tapping other sources of income, such as leasing its broadcast license and space in its studio. WFMU has an annual operating budget of $600,000.

''JM in the AM's'' audience of 54,000 represents nearly half of the station's total audience of 115,000, Mr. Freedman said, citing audited figures for weekly listeners.

Mr. Segal grew up in Newark, the son of Zev Segal, the rabbi of the Young Israel of Newark. Nachum is the fifth of six children in his family. He discovered radio at Yeshiva University, where he became the general manager of WYUR, the Yeshiva radio station. In 1983, during his senior year in college, he became host of the Jewish morning show at WFMU that later became ''JM in the AM.''

He stands out at the station, and not just because he is 6 feet 6 inches tall. One recent morning, he arrived at work at 6 a.m. in a long-sleeved white shirt with a dark tie. Atop his head was a black knit yarmulke. Mr. Freedman, the station manager, arrived a few hours later, hatless, wearing shorts and a t-shirt. He quickly excused himself to go out and clean up garbage that was strewn around the parking lot.

Inside the studio, Mr. Segal prays. An Orthodox man is obligated to pray each morning wearing a prayer shawl known as a tallit and leather boxes containing verses from scripture. These boxes, known as tefillin, are affixed to the arm and head with leather straps, an outfit that reminds some of a blood pressure apparatus. With delight, Mr. Segal tells how one morning a station volunteer entered the studio during the prayers and, startled, asked, ''Medical or spiritual?''

''Aside from the question of, 'How do you make a living?' the question I get most often is, 'When do you daven?' '' or pray in yiddish, he said. ''The answer is: before, during or after the show.''

At times, it's during. Mr. Segal will pray while he plays the long sets of music that run from 6 to 7:30. ''People like to wake up to music,'' he said. The last hour and a half, his prayers finished, he spends much more time talking.

With a rapid-fire delivery, he'll use Yiddish and Hebrew words like rebbetzin (a rabbi's wife), mishpocheh (family), halacha (Jewish law) and nusach (liturgical formats) without explanation. Expressions like ''shalom bayis'' (marital harmony) and ''baruch hashem'' (thank God) roll off his tongue. His audience understands him and he understands his audience.

He will announce events like the Yeshiva of Flatbush carnival, the local fundraising dinner for Shaarei Zedek Hospital in Jeruslaem and a lecture on the 2000 election called ''Is It Good for the Jews?''

He will then turn back to music, playing CD's by groups like the Diaspora Yeshiva Band, Regesh, Journeys, Shlomie Dachs, Avraham Fried and the late Rabbi Shlomo Carlebach.

Mr. Segal will take another break to talk about the issues of the day that concern the Jewish community. He does his best to keep neutral on most issues, he says, by inviting community experts to address them. One frequent guest is Malcolm Hoenlein, the executive vice chairman of the Conference of Presidents of Major American Jewish Organizations.

''I get more reaction from my appearances on 'JM in the AM' than I do from CNN,'' Mr. Hoenlein said. ''Nachum has a committed audience, more oriented to the issues I discuss. People remember what you say on the program. It's an unusual phenomenon.''

Mr. Hoenlein said that he believes the show reaches ''beyond the Orthodox world'' and, because of its presence on the net (www.jmintheam .org), well beyond New York. ''When I go to a federation event or speak at a non-Orthodox synagogue in different parts of the country, people come up to me all the time and say they heard me on Nachum's show.''

In recent months, Mr. Hoenlein appeared on the show to discuss the Camp David summit that failed to produce an agreement between Israel and the Palestinians and to discuss the selection of Senator Joseph I. Lieberman as the Democratic vice presidential candidate.

Most often, Mr. Segal initiates the appearance of Mr. Hoenlein, inviting him to spend some time with him in the studio or by phone. But Mr. Hoenlein recalled at least one instance when he requested air time. When 13 Iranian Jews were first arrested last year and charged with espionage, Mr. Hoenlein said that ''we were having trouble getting the general media to pay attention.''

''I called Nachum and said I wanted to go on the air. He gave me a platform and I reached my core audience.''

Typical of the ''core audience'' might be Ruchie Robinson, a bookkeeper in her husband's mail-order business, who lives in the Borough Park section of Brooklyn. She and her husband, Michoel, have five children, ranging in age from 2 to 12. ''Nachum does a nice service for the Orthodox community,'' she said by telephone as her children were having a lively dinner in the background. ''I can turn him on and not worry about what the kids will hear. And I don't even mean what Clinton did in the White House, but even about rapes, murders and people being thrown off subway platforms.'' The Jewish music that Mr. Segal offers on the air, she said, is a vast improvement on the rock 'n' roll and rap music offered on other stations.

''I almost consider him a friend,'' she said of Mr. Segal. ''I can't have a baby or celebrate a birthday without him. If it's not on 'JM in the AM,' it didn't happen.''

Mr. Segal creates a sense of community by offering ''mazel tov'' wishes on the air between songs. Birthdays, anniversaries, weddings, engagements, all get air time.

MR. SEGAL estimates that just over half, perhaps 55 percent, of his listeners are women. Orthodox men and boys are more likely to spend their mornings in the synagogue or in the study halls than listening to the radio. Still, he only occasionally plays music by women, such as the American Neshama Carlebach or any number of popular Israeli singers, such as Shoshana Damari, Chava Alberstein or the late Ofra Haza. Mr. Segal admits to getting pressure from the more traditional elements of the Orthodox community not to play women, but says he gets even more calls from those who want women. ''Go try to satisfy the tastes of everyone in this audience, I challenge you,'' he said.

While he tends to favor the right wing, he has also given a platform to the left wing of Orthodoxy. Among the modern Orthodox groups to which he's given air time are Edah, whose slogan is ''The Courage to be Modern and Orthodox,'' and a group called the Jewish Orthodox Feminist Alliance. He is also an ardent Zionist, even though some of his listeners are more neutral on Israel, believing that it is improper to establish a secular government there before the coming of the Messiah.

Nonetheless, he ends every show with the melody of Hatikvah, the Israeli national anthem, and intones: ''Our brothers and sisters in Israel, we are with you.'' Three of Mr. Segal's siblings live in Israel with their families.

Mr. Segal and his wife Staci have five children, among them a set of triplets. Two of the triplets are boys and their bris in 1998 was broadcast -- live -- on ''JM in the AM.''