The book business is turning into a lucrative sideline for some members of the Supreme Court -- especially Justice Clarence Thomas.

Historically the least wealthy justice on the high court, Thomas took a giant leap in personal prosperity last year, thanks to a large infusion of cash from HarperCollins, the publisher of his forthcoming memoir. The book is being touted as an emotional tale of Thomas's rise from poverty and is sure to include his account of the all-out battle over his confirmation in 1991.

On April 16, 2003, Thomas received $500,000 from the Rupert Murdoch-controlled publisher, according to Thomas's just-released financial disclosure form covering his 2003 activity. It was the first publicly acknowledged installment of a deal that will eventually pay Thomas a seven-figure sum.

The amount is more than twice Thomas's official salary as an associate justice, which is $194,000 a year. Still, it is unclear precisely how much the additional income affected the justice's net worth, since he reported the same level of assets as he did in 2002, between $150,000 and $410,000.

Justices are required to report only a range of values, not a precise amount, and they are not required to report the value of their homes. The reports for 2003 were released Friday.

Federal law prohibits the justices from making more than $23,000 from teaching and other outside sources each year. But there is no limit on book earnings.

Before Thomas's contract with HarperCollins -- the largest book deal ever for a sitting member of the court -- the justices who had made the most of this exception were Chief Justice William H. Rehnquist and Justice Sandra Day O'Connor. And both of them were back in business in 2003, with Rehnquist reporting more than $35,000 in book-related income, and O'Connor registering $9,950, according to their disclosure forms.

Rehnquist, who earns $203,000 as chief justice, just completed a round of interviews to promote his latest historical book, "Centennial Crisis," which is about the disputed presidential election of 1876.

His disclosure form says that he received a book advance of $25,000 from Alfred A. Knopf, the publisher, on March 21, 2003, along with two royalty payments totaling more than $10,000, also from Knopf. He received similar payments in 2002.

O'Connor made extra money from creative spinoffs of books she has already published.

Random House paid her $5,000 to record an audio version of her 2002 book, "Lazy B," a memoir, co-written with brother Alan Day, of growing up on a ranch in the desert Southwest. This followed a similar payment of $5,000 in 2002.

Not counting the recording fees, "Lazy B" earned O'Connor about $143,000 in advances and royalties, according to past disclosure forms.

She derived an additional $4,950 in 2003 from a second book, "The Majesty of the Law." Published last year, the collection of essays did not profit O'Connor directly because she pledged her share of the proceeds to charity.

O'Connor made the money not from the sale of the book, but from the sale of title pages that she had autographed. They were bought by MBI, a Connecticut-based direct-marketing company that sells leather-bound books as well as items such as limited-edition die-cast Model T replicas and dolls of the Old South.

MBI included the O'Connor-signed pages in leather-bound editions of "The Majesty of the Law," which it sold for $90 each through its Easton Press catalog, said Roy Pfeil, publisher of Easton Press.

According to Pfeil, O'Connor joined the ranks of other famous figures who have cut such deals with MBI, including former presidents Gerald R. Ford and Jimmy Carter and former British prime minister Margaret Thatcher.

O'Connor also picked up $18,000 from the American Philosophical Society, which gave her its Benjamin Franklin Award for Distinguished Public Service.

The additional earnings may have helped O'Connor weather a recent downdraft in the stock market: Her disclosure form shows that she lost an unspecified amount of money on the sale of shares in Cisco, Federal Home Loan Banks, Qualcomm, Agere and Sun Microsystems.

Still, she and her husband, John, a lawyer, own assets worth between $2.6 million and $5.9 million.

Other justices who reported assets worth at least $1 million included Stephen G. Breyer, Ruth Bader Ginsburg, David H. Souter and John Paul Stevens.

Justice Sandra Day O'Connor draws income from sales of autographed title pages and spinoffs of her published work.Justice Clarence Thomas received $500,000 last year.