The young man standing before the Greenwich (Conn.) Reform Synagogue Congregation Saturday chanting in Hebrew for his bar mitzvah wasn't all that young. It was 48-year-old television sportscaster Warner Wolf, who like any 13-year-old being bar mitzvahed had spent a year studying Hebrew for this special occasion.

A Washingtonian who became a media celebrity at Channel 9, Wolf is now a sportscaster on WCBS in New York and appears on Fridays on "CBS Morning News." He said yesterday it had bothered him for years that he had never had a bar mitzvah and was reminded of it when he escaped a serious accident in New York last year. "I decided that God was showing me that you could go at any time and if you are going to be bar mitzvahed, you'd better do it."

Describing the bar mitzvah as the greatest experience of his life, Wolf said he did it because he didn't want to be the only Wolf in his family not bar mitzvahed and "I wanted to reaffirm my commitment as a Jew and it was my personal commitment to Soviet Jewry and for that Soviet Jew who would like to be bar mitzvahed, but the Soviet government won't allow it." One of Wolf's Washington friends, Lew Citren, owner of Ace Wrecking Co., remembered that Wolf had been at his bar mitzvah and it had taken "35 years to get invited to yours." Tax Reform -- One for the Books

A few years ago, even last year, the idea of income tax reform seemed remote. But if the Senate votes as expected today to approve a reform package, the unexpected will be that much closer to reality. Just how tax reform came about is to be the subject of a Random House book, for which agreement was reached yesterday. It will be written by Wall Street Journal economics reporter Alan Murray and congressional reporter Jeffrey Birnbaum. Al Hunt, The Journal's Washington bureau chief, will write an introduction.

Peter Osnos, Random House associate publisher and senior editor, said yesterday that the book, expected to be published in the spring, is the kind of story of "lasting historical value, especially right now when all the principals involved can be carefully debriefed." Hunt says the book will show the power of an idea and the power of personalities such as Treasury Secretary Jim Baker, White House chief of staff Donald Regan, Sen. Bill Bradley and Rep. Dan Rostenkowski. End Notes

"Death Valley Days" isn't on television anymore, but President Reagan still has a favorite program. At a White House ceremony yesterday honoring 141 presidential scholars, high school students who have achieved recognition for academic, artistic and leadership endeavors, Reagan said, "I draw even greater encouragement from the signs that the wider culture is once again beginning to respect, even to celebrate family life. It is no accident that 'Family Ties' is my favorite TV show." It's been a good year for Michael J. Fox . . .

With the long battle for tax reform almost over, Rostenkowski, chairman of the House Ways and Means Committee, hosted a thank-you steak dinner Sunday night for 100, including members of the committee and staff and spouses, at Morton's in Georgetown . . .

A group of Gaylord Nelson's former Senate colleagues showed up at Sen. Thomas Eagleton's Spring Valley home Sunday to observe Nelson's 70th birthday. Among the guests honoring the Wisconsin Democrat were Sens. Mark Hatfield, John Danforth, Donald Riegle, Dennis DeConcini and Jeff Bingaman, former senators Eugene McCarthy and Walter Mondale and former representative Ludlow Ashley . . .

Comedian Steve Martin, who is a trustee of the Los Angeles County Museum of Art, was in town yesterday to tour the Corcoran Gallery of Art with gallery Director Michael Botwinick . . .

Britain's leading opera house, the Royal Opera at Covent Garden, has announced that it is risking the "disgust" of the purists by using translated surtitles of foreign librettos. The Washington Opera has used surtitles above the stage during performances here and has earned much more praise than criticism for the improvement . . .