Rabbi Irvin Ungar is staring at an index card. "E=MC2" is scrawled on it, as is the signature of Albert Einstein. On a shelf nearby is one of four extant copies of the 1543 memoir "Travels of Rabbi Benjamin."

These precious treasures won't be with Ungar for long.

Ungar, former spiritual leader of Peninsula Temple Sholom and a professional collector of rare texts and manuscripts, is putting these two items up for sale at the International League of Antiquarian Booksellers Book Fair, set for Friday to Sunday, Sept. 6 to 8 in San Francisco.

"I look at myself as a caretaker. It's a privilege just to be able to handle such rare texts and place them in the proper hands," Ungar said from his Burlingame home office.

The Antiquarian Booksellers fair is no sisterhood book bazaar where the casual shopper can pick up a well-thumbed copy of Erica Jong's "Fear of Flying" for 50 cents or a tome of traditional Scandinavian folksongs for $2.

Instead, 175 booksellers will meet for the first time in 30 years on the West Coast of the United States. The members, who represent 20 countries and meet every other year, are offering rare finds like the earliest printed version of "Cinderella" by Geiler Von Kaiserburg (circa 1510) and an 1880 letter from Fyodor Dostoevsky to writer/journalist Viktor Feofilovich Putsykovich in which he discusses his work on "The Brothers Karamazov."

The selections range from law, architecture, economics and wine to children's stories and medieval maps. In addition, experts will appraise books for free on Sept. 8 from 1 p.m. to 3 p.m.

Among the Judaica offerings are "The Statute of Kalisz" by Arthur Szyk (Paris 1928); the complete transcripts of the interrogations of Adolf Eichmann, mimeographed and in their original wrappers; "Schunheit im Olympischen Kampf" by Leni Riefenstahl (Berlin 1936); and Ungar's items.

Such old and rare works command sophisticated prices . Ungar's 16th-century "Travels of Rabbi Benjamin" measures only five and one-half by four inches and is 32 pages long. But its asking price is $42,000.

"One of my clients joked that he could buy a new Porsche for the price of a book," Ungar said.

However, the book fair's clientele — mostly librarians, university and museum personnel and a handful of private collectors — doesn't seem fazed. After all, Ungar's clients have been able to add first-edition manuscripts by Mark Twain, Herman Melville and Nathaniel Hawthorne to their collections.

Ungar's offerings for the September fair include a first-edition presentation copy of the 1958 political debates between Abraham Lincoln and Stephen Douglas, signed by Lincoln. Only 24 signed copies are known to exist.

Also for sale is the No. 6 edition, dated 1947, of the Yiddish newspaper "Ba Derekh" ("On the Way"), published by Holocaust survivors interned in Germany after the war.

The newspaper's writers had fled Europe aboard the ship Exodus on their way to then-Palestine. In an effort to placate Palestinians, British troops brought the emigres onto English ships upon their arrival, sending them back to France and then Germany, where the newsletter originated.

Ba Derekh "was their news of the day," Ungar said.

Likewise, the writings of Benjamin of Tudela are up-to-the-minute reports on Jewish communities from Africa to China by a contemporary of Marco Polo. Written in Hebrew, the 1543 edition "is truly rare," Ungar said.

"His record is not of importance just to the Jewish world, but a fundamental account of European history."

It has since been translated into many languages.

Ungar purchased these manuscripts with no particular client in mind. He simply knew they were "important texts."

"You might have a book in mind for a client but it's not there. Or you may not have a client but you know an important book is available," Ungar said, pointing to Anne Frank's autograph, which he purchased and later sold to the Simon Wiesenthal Center in Los Angeles.

"This can't be done on a timely basis. But every day is an adventure. It's really exciting to hold a book signed by Lincoln.

"And it's your business to know what's available."