NEW YORK - Huguette Clark, a 104-year-old heiress to a Montana copper fortune who once lived in the largest apartment on New York City's Fifth Avenue, died yesterday at a Manhattan hospital.

The reclusive Clark spent the last two decades of her life in New York City hospitals, but Manhattan prosecutors are still pursuing a case over her money and care.

"Miss Clark's passing is a sad event for all those who have loved and respected her over the years," her attorney, Wallace Bock, said in a statement.

The statement was released by Bock's lawyer, Robert J. Anello, who declined to comment on a Manhattan district attorney's investigation into how Bock and Clark's accountant had handled her affairs.

The D.A.'s office is looking into claims made by Clark's family that she was kept isolated from almost everyone except Bock and her accountant, Irving Kamsler. They were in charge of a fortune estimated at a half-billion dollars.

Distant relatives said they never saw her, and feared she may not have understood decisions the two men made for her.

Clark inherited the riches amassed by her father in Montana's mining industry. William A. Clark was one of America's wealthiest men and built railroads across the country, founding Las Vegas in the process.

Huguette was born in 1906, when her 67-year-old father was a U.S. senator representing Montana and was married to a 28-year-old Michigan woman named Anna Eugenia La Chapelle. He died in 1925.

As of last year, his daughter still owned a 42-room, multifloor apartment at 907 Fifth Ave.; a Connecticut castle surrounded by 52 acres of land; and a Santa Barbara, Calif., mansion built on a 23-acre bluff overlooking the Pacific Ocean.

Beginning in the 1960s, after her mother died, Clark rarely left her Fifth Avenue home, having whatever she needed delivered there. She moved into a hospital in the 1980s.

Clark shunned most visitors and left decisions in the hands of Bock - from bidding on vintage dolls at auction to settling disputes among her nurses.

But Clark "has always been a strong-willed individual with firm convictions about how her life should be led and who should be privy to her affairs," Bock said in an affidavit filed in court last year.

The Manhattan D.A.'s office also prosecuted the case involving Brooke Astor, another heiress whose son was convicted of colluding with her attorney to steal millions from her.