On a recent chilly night, Saratoga's Congregation Beth David was filled to capacity with well-dressed and distinguished-looking individuals.

They were there for sex.

To be precise, they were there to learn about sex within the context of Jewish tradition from one of the foremost authorities on the subject: Ruth Westheimer. Appearing as a speaker for the Distinguished Lecture Series of the South Bay Institute for Jewish Living and Learning, "Dr. Ruth" talked about her 13th book, "Heavenly Sex," which she co-authored with Jewish Week editor Jonathan Mark.

"Heavenly Sex" is a Jewish road map of sorts, with Dr. Ruth offering examples from biblical lore addressing such puzzlers as: Which night of the week is best for making love? How often should couples have sex? Is premarital sex "kosher"?

Although the book is light in tone it does not shy away from controversy, offering readers the biblical perspective on heavy issues such as adultery, incest and rape.

Throughout the text, Westheimer maintains that God is the ultimate sex therapist and the Bible the greatest manual.

"There is a Bible in every motel in the country," she writes, "and quite rightly — the Bible is the oldest but still the wisest guide to sex ever written. People pick up the Bible for many different reasons but rarely, if ever, as a sex manual. That is their mistake."

Standing on a 2-foot-high booster, Westheimer offered sexual tidbits across a podium normally reserved for rabbis and youngsters having bar and bat mitzvahs.

"At what age is it `over' for a man?" someone in the audience asked sheepishly.

"The orgasmic response may not be as strong [after a certain point]," Westheimer replied, "but if people are happy and in love they can be sexually active. Look at Abraham and Sarah — they were certainly getting on in years."

Many asked questions that went beyond even a sage's ken. "Does size make a difference?" someone wanted to know.

"Sexual satisfaction is in the brain, so size does not matter," Dr. Ruth assured, but then added, "except if it's a minuscule one."

"What should be done when one partner wants sex more often than the other?" one guest inquired via a folded note. Presuming that the less interested partner is a woman, Dr. Ruth admonished: "How long does it take, two minutes? Then do it. One person should do something to make the other satisfied."

Sigmund Freud and a Yiddishe Mama rolled into one, Dr. Ruth first created a stir in 1980 with her radio program, "Sexually Speaking," and later launched the nationally syndicated TV program, "The Dr. Ruth Show." She is the president of her local YMHA and was executive producer for a documentary on Ethiopian Jews.

Behind the celebrated public persona is a young girl named Karola Ruth Siegel who was born in Frankfurt, Germany, in 1928. At the age of 10, she was sent to a Swiss orphanage, thus escaping the Holocaust in which every member of her family eventually perished. At 16, she fought for Israel's independence as a member of the Haganah.

Perhaps these early experiences influence her assertion that a healthy approach has made good sex possible for Jews in even the worst circumstances and situations.

"If a man and a woman are truly lovers, they can make their bed on the edge of a sword," Dr. Ruth said, quoting a passage from the Talmud. "If their love goes bad, the best bed in the world is not big enough."